I don't get any error messages when I launch PM a second time. If I close PM and try to launch it a second time, it won't launch. It appears to be launching in the dock because the little dot under it is blinking, but it never actually launches. In Force Quite Applications it shows as: "Photo Mechanic 5 (not responding)"
Coincidentally, when this happens, Finder also shows as: "Finder (not responding)". Relaunching Finder normally doesn't work. Using Activity Monitor, I can get Finder working again by force quitting WindowServer, but this only helps me to relaunch Finder. It doesn't help for relaunching PM.
The only way to relaunch PM after it freezes is to Force Quit and reboot. Upon reboot, I am able to launch PM again, but no error messages appear. Thanks again.