Perform a reboot of the Core machine and see if this resolves the issue. Before rebooting, please stop the Core services gracefully:
Perform repair of .NET Framework.
This Microsoft KB article may be resourceful: http://www.microsoft.com/en-us/download/details.aspx?id=30135
If the issue still persists, please complete the following:
If the issue still persist, please perform AppAssure Core Software repair from the Control Panel.