have a look at the referenced files. There are all your servers FM5.5 has ever seen. You should clean up those references and things go fine. The problem was gone with all the files I did convert.
Where do I find these references?
Open Manage | External Data Sources.
The two main culprits are references to IP addresses that are invalid, but are followed by a different reference in the same entry that works and references that use asterisks.
Brace yourself. Older versions of FileMaker did a really sloppy job of managing these and gave us no direct control of the references. You may find references to locations that haven't existed in your system for years and will likely find duplicate references to the same file, but with slightly different details in the external source references. While you can delete filepaths that are no longer valid, you can't just delete the entire extra reference without first tracking down each place that uses the extra reference and determining either that it's a part of the system you no longer use or one to update by "re-pointing" it at the other reference.
I was able to use FileMaker advanced to remove all such duplication, but it took repeated searches of a database design report to track them all down in my scripts and layouts.