usually that would occur when you don't have the extended plug-ins installed in the folders for exporting and/or importing. It also occurs if you don't have the add-ins installed. But mainly just the export and/or import issue. It MAY but not usually occur if you don't have the proper file formats and imaging formats installed.
it would have helped to know the MAC version to be more specific as to the error issue. Which is why I only gave a generalized response. You may also check the forums, we had a long standing thread on manga studio... Within which we discussed many issues for both the MAC and windows version, we also discussed a few differences to expect within EX and standard versions. I hope this helped a little if you are still having the error. By now you may even have already had it fixed. So later and good to be back all... Hope the old crew is still online.