You're the second case I've seen like this today.
Previous user was able to temporarily solve the problem by trashing prefs (see Replace Your Preferences) but it returned almost immediately and they ended up uninstalling, running the clean tool (Resolve installation problems with CS5 Cleaner Tool) and reinstalling. It's been several hours since I've heard from them, so I don't know if that is a permanent solution, but I'm hopeful.
Peter, thanks for your answer.
In my case it happened some days ago (using InDesign every day) and a few minutes ago for the second time. I think I'm going to reinstall CS6 indeed.
Replacing the prefs is a lot faster and easier, if it works.
Okay, then I'll try that first.
Some new information this morning from the other user:
Hi Peter, I just wanted to give you an udate in case it helps others: the problem returned, and I tried creating a new profile on my machine and running it that way, to see if it was just the prefs or my profile. Although i could save etc I then couldn't PDF anything without errors, so went back to my original profile. I reinstalled Acrobat in case that was the culprit, but no difference.
SO, I had a rethink and removed Magic Prefs which was running in the background, and also turned off Allow Multiple Gestures in Indesign prefs. So far all stable, and working well on big files across CS6, so hopefullly this has proved to be the fix.
Kind regards and thanks again for all your help and quick responses.
NB I am running CS on a new iMac running OSX 10.7.4. I use Font Explorer X Pro, Firefox, Filezilla, Picasa and Easyfind. No other third party software on my mac. I work largely off an external server.