I'm having this exact same issue...I get that "FileMkaer cannot share files because..." error message poppingup every time I open a file.
Having the same issue with FMP10 + Mountain Lion.
After years of struggle I convinced my boss to upgrade my machine and the server machine (previously both 10yr old PowerMac G5s) ... I'm not looking forward to breaking the news that that upgrade will necessitate a FileMaker upgrade, too!
The fresh, new, clean-installed Mac Mini w/ Mountain Lion can open .fmp7s locally but pops the alert when it does -- and when I go into the Sharing dialog and toggle the switch off and on it pops it again, and this pops up in Console.app:1/17/13 10:59:34.353 AM com.filemaker.messages: 2013-01-17 10:59:34.353 -0700 [AttachThread_ac8e0a28] ConstructORB() caught a CORBA INITIALIZE exceptionThe machine also seems to be unable to open files remotely hosted on our network. When I open the Open Remote... dialog I can see the remote machine but not the file it's hosting. This pops up in the console:1/17/13 11:20:39.917 AM com.filemaker.messages: 2013-01-17 11:20:39.917 -0700 [Draco::OmniThread] ConstructORB() caught a CORBA INITIALIZE exceptionI realize that FMP10 & ML are not a supported combination but any help would be greatly appreciated!
We're having the same problem with a Mac Mini in our post-production facility. It has nothing to do with Mtn. Lion as I'm running the exact version of FMPro (10.03) on the MacPro in my studio and Studio B can also access with the same Mac I've got.
The Mini can see the server but NONE of the files, so we moved the filed this editor needed all the time to his local drive. When he opens it he gets the error it's "being shared by someone else on this computer...".
Not sure what to do short of an OS re-install. I've uninstalled/reinstalled FMPro multiple times without any luck.
Any other ideas?