Symptoms

Users can't open any published app, error This program is blocked by group policy is thrown:

Cause

Security settings on RDS hosts or Remote PCs prohibit the launching of C:\Windows\System32\memshell.exe

Memshell.exe is the component of Parallels Remote Application Server responsible for starting published resources.

Resolution

Please configure Group Policy or other security technology (i.e., Applocker) being used