I am using BIAB 2010 under a Windows XP Home Edition Version 5.1 on an old machine (2.4GHz Celeron) with 2GB of RAM.

I, too, have trouble closing the program. I get the DIDN'T CLOSE PROPERLY error. It doesn't seem to be a huge problem, since files save okay.

It happened to me moments ago when I closed BIAB after I lost all sound. (No doubt it's the crappy sound "card.")

Upon restarting the program, I was back in business.