Hmm, perhaps there simply is a problem with the starting of those applications from within PhotoMechanic. If I understand correctly platti recently updated to a newer version of his editing software. Perhaps it is just a matter of incorrect file associations (e.g., still pointing to the old version)?
Have you already tried opening the files directly from a Finder/Explorer window? Does the file open then? And what happens if you try to open the files directly from e.g. CaptureOne or BibblePro5?
Let us know what works for you,
Hayo