The file ".pdm-links" should be discarded by the user periodically, because sometimes errors will be written into the file.  If a user wants to clear out their PDM-links it is much quicker to delete this file rather than point a Pro/PDM browser at their PDM-links and delete them selectively.  Sometimes Pro/PDM will crash out during the fetch process just when you are expecting the dialogue box which asks you to choose between "retrieve into Pro/E", "create local copies" and "create PDM links", and this is another time when the file ".pdm-links" should be discarded.  I usually move this file into a different folder, just to hide it from Pro/PDM, so that if it does not fix the problem I can put the file back again.