Open Manage | External Data Sources, You have a reference to an external file here that cannot find the external file as it has been moved, renamed, or an enclosing folder was renamed. Brace yourself, if the files were originally from FileMaker 6 or older, these external references may be very, very messy and you may need to spend some time carefully checking each. Once you update the problem external file reference so that it points to your current file (the one you are locating each time you open your database), this error dialog will no longer appear.
Worked great. Thank you.