I've decided to refresh this sticky as it was looking rather old.
In essence then, if you are trying to run BFD2 v188.8.131.52 (or earlier) in ProTools 8.x on Windows Vista or Windows 7, you need to disable UAC to prevent that nasty access violation error from popping up.
For your interest, we're currently working on BFD2 v2.2 and have re-engineered all of BFD2's registry and preference locations to comply with current UAC design guidelines. Recent testing has shown that latest v2.2 betas now play happily in ProTools v8.0.4 with UAC enabled (on both Windows7 x86 and x64 flavors), so with any luck this issue will be water under the bridge soon.
I still think you should disable UAC though.
"I was great engineer once, but then I took an arrow to the knee..."