The "privileges damaged or possibly tampered with" issue
For those who haven't run into this before, there's a security 'feature' in FMP that if the user/password info in a file gets altered (usually by file corruption), FMP refuses to open the file. You get this message:
"The access privileges in this file have been damaged or possibly tampered with. Please contact Filemaker Technical Support if the problem cannot be resolved." If you see this, you are totally hosed. Filemaker Technical Support cannot help you. The "Recover" command will not work in this case.
As far as I can tell - I've never gotten a definite answer one way or another - this is an entirely arbitrary decision made by the FM dev team. It's not a matter of whether or not the file can be opened; FMP is engineered to refuse to open the file if there's any alteration to the access privileges.
I understand the reasoning (I think I do, anyway). It's essentially a kill switch in case of an attempt to compromise the security of your data. Considering it's much more likely to be file corruption than Al-Qaeda breaking into your vinyl record collection index, it seems a bit draconian.
I wish there was an option to be warned about the access privilege corruption rather than a total lockout from the file. Something along the lines of "Hey, your access privileges have been damaged or possibly tampered with. Either way, you should really do something about that right now. Should I continue opening this file?" At least you'd get a fighting chance to salvage your data.