Hi Walt,
I had exactly the same problem yesterday – have been using Log and Transfer for C300 footage for nearly 2 years and no problems at all – but then all the symptoms you described appeared.
After trashing preferences, reinstalling Canon drivers, etc., no luck.
But today I checked my software updates and saw that I needed to update my ProApps Quicktime codecs. Installed the update and Log and Transfer works! (I believe the version I installed was 1.0.4 but I can’t be sure as I didn’t make a note of it.)
I hope this can help someone.
Best wishes,
Ed