It's not a standard Filemaker error message that I recognize. Any chance that there's a script using show custom dialog to pop up this message?
If so, you'll need to examine that script to determine why this is happening. You can launch FileMaker advanced without opening any files, then enable the script debugger, then use open file to open this file to watch for any scripts that might execute automatically when the file opens. Not only might this enable you to see what script is displaying this message, you can then use the debugger to halt the script before it closes the file so that you can then fix the problem.