1) another thing we can check is the exact properties of the new m2v files, and compare those side-by-side against the attributes of the old *original* m2v files (if you still have them / kept the raw source?)'
.... that way we can ensure that the encodings and formats are identical (or not).
then if that checks out, i'd suggest we move on to the next step.
Q: what format does your camera save them in? is it m2v, or is that something that gets converted later?
2) if you can locate a "backup configuration / preferences" in premeire, that would be good...
... and then we could attempt to delete / reset the config settings to default.
3) ... and then do the same thing with encore.
4) if none of the above works, and we can't find anything else to try, then we can look at doing a "purge" uninstall/removal of encore & premeire, and reinstalling from scratch.... i realize this can take hours to do, so i'd rather save it as a last resort.