While investigating fixes for some problems we were having in XenApp 6 we installed XA600W2K8R2X64068. After doing so we were experiencing a very high number of disconnected sessions and the users were not able to re-establish their sessions. There were many reports of users being unable to login, and we were seeing wfshell.exe crashes. We reverted to the previous PVS image that we had just before adding the XA600W2K8R2X64068 hotfix and all reported issues related to that changed stopped occurring. We have the following hotfixes installed along with Windows 2008 R2 SP1 and the system stability has been good.

XA600W2K8R2X64018 http://support.citrix.com/article/CTX127023
XA600W2K8R2X64010 http://support.citrix.com/article/CTX126490
XA600W2K8R2X64012 http://support.citrix.com/article/CTX126679
XA600W2K8R2X64017 http://support.citrix.com/article/CTX126958
XA600W2K8R2X64021 http://support.citrix.com/article/CTX127036
XA600W2K8R2X64026 http://support.citrix.com/article/CTX127360
XA600W2K8R2X64029 http://support.citrix.com/article/CTX127405
XA600W2K8R2X64056 http://support.citrix.com/article/CTX128945
XA600W2K8R2X64062 http://support.citrix.com/article/CTX129278