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Exchange 2013 CU6: Don’t deploy in Exchange 2007 mixed mode and Hybrid

Microsoft recently released Exchange 2013 CU6 which is fixing a lot of issues which were coming in CU5. My Lab installation on new server went very smooth.


Exchange 2007 Mixed Mode issue

While I tested DAG, mailflow and run other test, people reported the issue with the Exchange 2007 mixed mode.

In Exchange 2007 mixed mode, the issue reported as an issue with databases flapping which was due to exchange 2007 mailboxes are talking to exchange 2013 mailboxes.

We reported the issue to Microsoft and Microsoft confirms that there is an issue which happens when exchange 2007 server user attempts to access a delegated mailbox that is on exchange 2013 server.

Microsoft is tracking the issue by KB2997209 which is still being published.


Hybrid Issue

Meanwhile Microsoft MVP Jeff Guillet also reported another issue in Hybrid environment. To know more about this issue. Please have a look here.


Microsoft decided to continue working on this issue even over the Labor Day weekend.

We expect that Microsoft will fix these issues in CU7. In the meantime, we recommend exchange 2007 mixed mode and hybrid customers do not deploy CU6 at this time and wait for Microsoft’s update.


Microsoft team blog link:


Update at 5:00 PM – Microsoft has released the update. Here is the link. Ryan has tested it and it has fixed the issue. 


Prabhat Nigam

Microsoft Solutions Architect | Exchange Server


34 Responses to “Exchange 2013 CU6: Don’t deploy in Exchange 2007 mixed mode and Hybrid”

  1. Ryan Says:

    Fyi, we’ve just had the fix and everything is running smooth again.

  2. Prabhat Nigam Says:

    Exchange 2007 KB released –

  3. Prabhat Nigam Says:

    To fix the issue with Hybrid, MS has released the script but the script needs to be updated.

    Update the script if exchange is not installed in the default c drive path.
    $baseDirectory = “$Env:ExchangeInstallPath” +”ClientAccess\ecp\DDI”

  4. Thomas Lhadnif Says:


    I am running 2007 in co-existence and I am planning to deploy the update + kb2997355

    In another thread someone mentioned a bug with activesync proxy. Is this still the case ?
    We have a lot of activesync users on 2007/2013 so we can not break all the 2007 users if we deploy this.

  5. Prabhat Nigam Says:

    Marcus has reported this issue but Microsoft has not confirmed it yet. I would recommend testing in the lab or holding the migration until we hear from Microsoft.

    I will update here.

    or you can check here –

  6. Vince R. Says:

    We actually deployed CU6 on one mailbox server and we had to call support to run the hotfix. It appeared that everything was good but a new issue is now occurring and we were able to reproduce the same issue in test environment.

    The problem is that when a person accesses their mailbox via OWA they cannot reply or create new messages. And, the problem is when we apply the CU6 interim update (hotfix). When we moved the DBs with many of our users and they began to report the issues.

    The test environment we have is a similar setup to our production and it already had CU6 installed and working. We then updated one of the mailbox servers to the interim CU6 update and when a DB is activated on it and a user on that DB uses OWA, OWA does not work correctly.

  7. Vince R. Says:

    It appeared that everything was good after the hotfix but a new issue is now occurring and I was able to reproduce the same issue in my test environment.

    The problem is that when a person accesses their mailbox via OWA they cannot reply or create new messages. And, the problem is when I apply the CU6 interim update. When I moved the DBs with many of our users, they began to report the issues.

    The test environment I have is a similar setup to our production and it already had CU6 installed and working. I then update one of the mailbox servers to the interim CU6 update and when a DB is activated on it and a user on that DB uses OWA, OWA does not work correctly.

  8. Prabhat Nigam Says:

    Do you have CAS and Mailbox on the same server?
    If yes then could you do https://localhost/owa and tell me the outcome.

    If answers is no then I would say we should update CAS server as well. check if this helps in the lab.

  9. Vince R. Says:


    We were able to duplicate the problem in our test environment. We have 4 servers (2 CAS Servers and 2 Mailbox). We updated CU6 on all 4 servers. We applied the hotfix on only one of the mailbox servers. Users who are on that mailbox server with the hotfix have the OWA problem. Also, I forgot to mention that the Microsoft engineer had us run the Strong Name tool. This is the command we used: sn.exe -Vl -Vr

  10. Prabhat Nigam Says:

    are you talking about hotfix 2997209 –

  11. Vince Says:

    Yes that’s exactly the hotfix. I forgot to mention we also have an all in one exchange 2007 server in our lab to simulate the 2007/2013 mixed mode.

  12. Prabhat Nigam Says:

    In your lab, could you install the hotfix on all servers and let me know if you are still facing the issue.
    Please also share the details of the OWA issue like, what is the problem, page is not opening or and error popup.

  13. Prabhat Nigam Says:

    Here is the Update from MS
    We will be publishing KB2997847 later today for the 2007/2013 EAS proxy issue. All customers can now request a combined fix for both 2007/2013 co-existence issues. Both of these fixes will be available in our next cumulative update.

  14. Brett B. Says:

    @Vince R. – I’m having the same problem. Compared 2 servers (one working, one not) and found that :\Program Files\Microsoft\Exchange Server\V15\ClientAccess\Owa\prem\10.0.995.31\ is missing nearly a thousand files. My lab/test servers are working fine so I can’t test against them right now, but my thought is copying them from a “working” server may resolve this. I should be able to confirm this tomorrow after my emergency maintenance window tonight.

    Also noticed some services after the Hotfix install were shown as “Disabled.” Leads me to believe the hotfix may bomb out without sending feedback to the user or install application. When I saw the services fail to be set back properly to Automatic start, I re-ran the hotfix after a reboot and it appeared to have worked for at least that portion of it – this happened on 3 out of the 6 servers (CAS/Mailbox Combined) on which I ran the hotfix.

    Has anyone else seen these issues?

  15. Vince Says:

    That’s it, the only difference is that we have 15.0.995.30 and not the 15.0.995.31. What we tried was to stop World Wide Web Service then rename the 15.0.995.30 version to 15.0.995.30_Original. Copied the 15.0.995.29 into a new folder and renamed it as 15.0.995.30. This way the 15.0.995.30 contained the files from the 15.0.995.29 version. Started the WWW Service and OWA seemed to work OK. This process was as per request from a Microsoft specialist who we still have an open phone call.

    We talked to him yesterday and we have a scheduled call for 2PM today. I will post what we do as soon as I have some other details.

  16. Brett B. Says:

    This may/may not be related, but I’ve noticed it on servers that were installed as SP1->CU5->CU6. The servers that were installed with CU6 without upgrade and then had the hotfix added in don’t seem to be missing those files. Your MS rep may be interested (or not?) in that.

  17. Vince Says:


    Yes Indeed! That is how we have done it. We’ll mention it to the rep when we manage to get in touch with him. In the mean time the version folders swap seems to fix the problem. We just don’t know if that is the way to go yet.

  18. Prabhat Nigam Says:

    Thank you Vince and Brett for updating us. Please continue to update us.

  19. Brett B. Says:

    Without requiring downtime or service restarts, I copied [InstallDrive]:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\Owa\prem\10.0.995.31\scripts\ from a known working server to the upgraded servers that weren’t allowing many OWA actions to complete. I didn’t overwrite any existing scripts and this folder appears to have only non-compiled JS.

    Did this after finding the following in my browser’s dev tools view:
    [… Failed to load resource: the server responded with a status of 404 (Not Found)
    Fail to load script en/…]

    Since they are non-compiled files that were just missing, no iisreset or app pool recycles were necessary. Browsers mostly picked it up immediately – some users had to clear their browser cache.

  20. Jacob Lund Says:

    We are having the same issue with Exchange 2013 CU6 with FIU to fix exchange 2007 coexistence issue. Was having database dismounts until hotfix. Now cannot create, reply, or forward emails. Also noticed that the “display settings” link doesn’t work anymore. Tried swapping the files but this was not successful. Does anyone have a known working copy of the files they can zip and send to me?

  21. ankit Says:

    can someone send me this hot fix? i have having same issue but don’t have support.

  22. Prabhat Nigam Says:

    You might need to open a free ticket with Microsoft. Microsoft should not charge you for this. Call Microsoft Australia.

  23. Ankit Says:

    Thanks Prabhat
    i tried to call them but i need agreement no/MSDN no. which i do not have.

  24. Prabhat Nigam Says:

    Try this –;%5BLN%5D;1422

  25. Ankit Says:

    I sent request. i will wait until microsoft respond.
    thanks Prabhat.

  26. Tom Lammers Says:

    Anyone have KB2997209? Need it.. Microsoft taking to long

  27. Alejandro Romero Says:

    Hi. I have just applied Hot Fix KB2997209. DB dismounting problem was solved, but OWA and ECP crashed.

    Anyone with the same experience?

  28. Kyle Green Says:


    I experienced the same issue this morning, copying/renaming the contents of the 15.0.995.31 folder did not work for me. I’m in the process of opening a support case now on the issue, did you ever get the issue resolved?

  29. Arno Rommens Says:

    Does someone have KB2997209 hotfix on a mirror site? Please contact me if you have it arommens @

    Thanks in advance.
    We have a mailserver which is down…

  30. Kyle Green Says:

    Careful deploying the hotfix, it breaks OWA and ECP, see my post about my experience:

  31. Serkan Mutlu Says:

    Did anybody solve the OWA problem after KB2997209 ? Arno Rommens I have this update If you want I can send it to you. But after install this OWA crashes.

  32. Serkan Mutlu Says:

    Vince R your solution worked for me. Thank you.

  33. Christian Says:

    I have installed the Interim Update for our Exchange.
    Now i want to install CU7, do i have to uninstall the update first?

  34. Prabhat Nigam Says:

    No you don’t need to uninstall.

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