Systems running Windows Server 2008 R2 products and Citrix XenApp 6.0 can experience unexpected termination of the UxSms service during user session logoff. UxSms is a component of the "User Desktop Experience" server feature required by XenApp.
Under certain conditions, it is possible that an invalid memory reference can occur in the UxSms service during a user logoff. This memory reference will eventually lead to termination of the service. The only known method of recovery is to restart the operating system.
This issue is known by Microsoft and currently there is no fix or work around available. Should you require further assistance with this this issue it is advised that you contact Microsoft referencing this article at 1-800-MICROSOFT.
for other considerations.