Issue
When trying to shadow users with multi-monitors you get an Error Code 120.
Resolution
There is no Citrix resolution for this, it’s a Microsoft RDS issue which effects XenApp shadowing (http://support.microsoft.com/kb/2484290)
Microsoft workaround for this is to install Remote Assistance and use this tool for Shadowing (http://support.citrix.com/article/CTX125693)
