I never used to have a problem opening up multiple instances of PT2; I'd usually leave one minimized with auto-imports running and then open another instance when I wanted to open another database/look at stats/etc.
For the past month? or so, about 70% of the time I open a new instance of PT2 when one is already running, it freezes shortly after opening (after the warning box about PT already being open and after the application appears, but before I have a chance to access menus or anything). I remember behavior like this happening before when there was a problem with the update/reg/whatever server, but if I leave the program sitting there for a long period of time it will never recover (whereas if it was some kind of server problem it would obviously time out eventually and let me use the program).
