Cannot connect to the Citrix XenApp server

I received a call early this morning asking for help on Citrix access problem.  Users were able to logon to the Citrix Web Interface but when they try launching any application, they were getting the following error.

Cannot connect to the Citrix XenApp server.
Protocol Driver error.

I RDP into the Citrix server and took a look at the event log and saw repeated error log on “Reliability Server” with the following message.

Unable to connect to the CGP tunnel destination (127.0.0.1:1494)

Then I remembered about the security patch MS12-024 breaking ICA and RDP connections which I have blogged about in April.

Microsoft Patch MS12-024 might break ICA and RDP connections of Windows Server 2003

I installed the hotfix 938759, rebooted the server and it fixed the problem.

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