Just a thought ...
This may help!
Uninstall the Beta Version of Photoshop CS6 now and then restart your computer and see if that works.
Open the CS5 Master Collection programs and see if that fixed the problem and it is all working as it should again.
A similar problem has also happened to a CS4 User and I just now made this suggestion to them as well.
It is worth a try!
All the best.
I have the PSCS6 beta on my mac and windows computers both with MC 5.5 running without any hitch.
Maybe a reboot is in order?
Perhaps you could try resetting the preference files for some of the apps and see if that resolves the false starts.
Else fails, try Tracey's suggestion above.
The first thing I did after I realized that CS5 wasn't working was to restart the computer. Did it twice, just in case. Still had issues, so I uninstalled the Beta and restarted. Still had issues. So I uninstalled all the CS5 programs, restarted, and reinstalled. So far so good.... Hope this helps.