This one had me going for a while. Citrix XenDesktop – VM Hosted Apps won’t work anymore when RES Workspace Manager gets installed. RES had an article “Q203249” that describes how to get it working. But both options in this article won’t work with Citrix XenDesktop 5.6 FP1, Windows 7 SP1 and RES Workspace Manager 2012.
After some chitchat with RES Support, they reproduced the error.
Only use the second option from the article, and from that part, only set this registry key:
HKLM\Software\RES\Workspace Manager Value: ResetCitrixExplorerHook Type: REG_SZ Data: No