I came across this issue recently when deploying a new Citrix XenApp 6.5 farm on Windows Server 2008 R2 and just wanted to make a quick note in case anyone else runs into it!
The Citrix XML service was not working on the first server in a new Citrix XenApp 6.5 farm I was building. When connecting to http://localhost/Scripts/ctxsta.dll in a browser I was receiving the following error:
HTTP Error 500.0 – Internal Server Error
There is a problem with the resource you are looking for, so it cannot be displayed.
Error Code 0×80070002
It appears that for some reason, the resource folder had not been copied into the C:\inetpub\Scripts directory by the XenApp 6.5 installer.
To fix I simply copied the resource folder from C:\Program Files (x86)\Citrix\system32\ to C:\inetpub\Scripts\
Once copied I restarted IIS by typing iisreset in a command prompt.
You should now receive the following message when connecting to http://localhost/Scripts/ctxsta.dll which shows that the Citrix XML service is working correctly:
HTTP Error 405.0 – method not supported
The page you are looking for cannot be displayed because an invalid method (HTTP verb) is being used.
Error Code 0×00000000