Thank you for your post, and I apologize for the late reply.
I have FileMaker Pro 10.0v3 running on a MacBook Pro with Mac OS X 10.6.8 installed. You did mention that you reinstalled FileMaker Pro 10, so it appears there is something in the System that is not allowing FileMaker Pro to evern restart.
Assuming no other applications are currently open and/or interfereing with FileMaker Pro, it could be that the Security Update did not install properly. You may have to reinstall Mac OS X 10.6, and then apply all the updates again.
I know almost three months have passed, so if you did find the cause, please post here so that others having a similar issue can benefit.
Thanks for the reply, and yes, in fact that was the problem - you are exactly right. As it turned out, over the course of several days, we discovered several other weird issues, ranging from other programs not opening to simple cosmetic issues like a single button graphic that no longer appeared in another program. I don't know why or how the update didn't install properly, but it was just the latest in a string of small but weird problems we had had with that particular machine, going back 18 months.
BTW, Because of the previous issues, and my persistence in troubleshooting and reporting, Apple actually ended up replacing the whole computer - a rare occurance, as I understand it. Apple lemons are rare, but they do exist and it seems we had one. Our replacement is a dream; we've had no problems to date. We are still running Filemaker 10, and have had no further issues. A word of advice to anyone with unresolvable Mac system issues - report them and keep reporting them to Apple. Do all the troubleshooting they ask you to, and report back if it doesn't fix the issue. If it ends up being hardware-related (as ours clearly was), the "paper" trail will be invaluable.
TSGal, thanks so much for the diagnosis and reply.