If an application (like ACT or Quickbooks Hangs up, it is usually either the application has stopped responding or a dialog box is awaiting your input.
It's important to observe what the last thing you were trying to do was.
If that does not resolve the issue, you can open connection manager and terminate the application.
To open connection center, look for the Citrix Icon in your system tray (for a Windows machine, down near the clock look for the blue and white Citrix icon,
Right click on the Citrix Icon and from the short manu, choose connection center.
Within the connection center, you can select the application that appears hung, then select terminate.
Choosing Log off will log you off of all applications.