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Exchange 2013: ActiveSync Not Connecting Error 12002

Today I was part of a critical change with one of my customer and witnessed this so sharing it for one and all.


We planned for a simple change of ActiveSync cutover from Exchange 2007 to Exchange 2013.

We updated the Externalurl of Exchange 2013 Internet facing servers.

We removed Externalurl of Exchange 2007 Internet facing servers.

We enabled windows integrated authentication on old Exchange 2007 Internet facing servers.

No Windows Integrated Authentication for Exchange 2013 internet facing servers.

We had NetScaler which had VIP configured for Exchange 2013 internet facing servers.

So everything as per books.



After changing the NAT pointing to Exchange 2013 VIP. ActiveSync stopped connecting.

When we ran the for ActiveSync connectivity, we got the following error.


“Client certificate authentication couldn’t be determined due to an unexpected failure occured. Winhttpresponse failed with the error 12002”



We were able to trace Exchange active sync traffic was coming to the NetScaler and there was nothing in the IIS Logs.

Error 12002 means The request has timed out.

So we were sure we had an issue before reaching Exchange 2013 servers.

We ran the TCPtrace which showed return traffic.

Network lead reviewed the configuration of the Netscaler and figured out that netscaler rule/VIP was configured for port 443 with HTTP.

We change it from HTTP to SSL.

Save all configuration.

The issue got fixed.


Prabhat Nigam

Microsoft MVP | Exchange Server


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