I've experienced the same problem with Studio Ultimate 12.1 importing from a Canon HV20 using Vista x64.  I've also started getting a message that my video card doesn't have enough graphics memory to support HD.  (It does, and Pinnacle support even agreed that it does.)  However, HD capture didn't work before the message either.  I've chatted with support several times over the past couple of years (and past few product versions), without any success.  They eventually ask me to send a sample HD movie. (Duh!  If I could, I wouldn't be calling them with problems with HD capture.)  Like you, I can import anything I want until I attempt HD.

 What's odd in my situation is that on rare occasion, I've been able to import HD without any problems.  I've tried removing any software/codecs which could be conflicting, and have re-installed the software (with their clean-up procedure) several times.  I've re-installed the graphics drivers and everything else they suggest.  Nothing has fixed the problem.

I'm extremely frustrated that they acknowledge a problem, but never seem to be able to pinpoint it or correct it.  I'm really tired of purchasing version upgrades in hopes of correcting the problem, only to find nothing has changed.

If anyone knows of a product which reliably captures from an HV20 on Vista x64 with a decent feature set, I'm interested in switching.