Do you know if Acu Connect has a time out setting.  If AcuConnect thinks that an AcuThin session is no longer running so it just disconnects the session.
 
Scenario is a program is running that has a lot of records to process so is running for a long period of time - then without any error messages the AcuThin session is disconnected (program and menu programs are gone), user is sitting back at desktop.