XenApp 6.5 - Unable to install the hotfix
installation fails because CDFSVC fails to start
If you compare a working and non-working machine you'll see some registry keys missing for cdfsvc
If you search the AppID, you might not find it on the problematic machine (HKCR)
in dcomcnfg you will not be able to see cdfsvc
 
 

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Instructions

browse to the location of cdfsvc in cmd
the location is "program files (x86)\Common Files\Citrix\System32
run cdfsvc /service
restart the machine
install the hotfix 

You may not be able to install XA HRP on the server, because the installer failes to start cdfsvc in the background If you try to start the service manually, the service fails with error Error 1920. Service 'Citrix Diagnostic Facility COM Server' (CdfSvc) failed to start'. Verify that you have sufficient privileges to start system services