Help! I can't *Close* my file(s)!

[Wickerman]

THis is a new one for me. I've been working on a file today for several hours in no particularly unusual way. (FMP 12 Advanced) -- the solution has been open all day, i closed the file but not the software for a break.

Upon return I re-opened the File, and now it's not letting me click into any of the layouts -- I can shift from Browse to layout mode etc, and the menus work, but I can't enter fields, and can't select anything in Layout. Worst of all, I can't close any windows or quit the program! These options are 'greyed out' in the menus and keystroke commands are impotent too.

For an experiment I tried opening another (unimportant) file on my desktop, and it's behaving the same way.

Am I doomed to perform a 'Force-Quit'? It's not a problem because I have hourly backups so at worst have lost a small amount of work.

I'm more concerned about why this has happened and how I might prevent a recurrence?

Mac OSX 10.7.4

FMP Advanced 12.0v1