Citrix has released information on recommended operating system patches from Microsoft which have been known to resolve issues within provisioned XenApp environments. Customers who experience any of the issues listed here should install these patches. The possible issues include:

Gray or black screens at boot time
Event ID 7011 in the event logs of the XenApp server, resulting in problems starting the network services at boot time

Recommended patches

https://support.microsoft.com/kb/981166
https://support.microsoft.com/kb/976674

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