As you are moving into upgraes to Version 2013, or putting the latest SU on Version 4.4, in my case SU 20 one workstation when opening MAS90 and then attempting to get into any module would automatically reboot. To resolve this Turn off PEP. To do this open MAS as Administrator, click on Sage Product Enhancement icon, then uncheck Participate in the Program, resolve my issues. This is in engineering so a fix maybe out soon.
Ron