Dionin - I've had much the same problems - also on Windows 8 64 bit - and in the end I've just uninstalled Sampletank completely.

However, if you run BIAB as "Administrator" you probably won't get the Access Violation error (at least I didn't).

On the other hand, I'm now getting other errors in BIAB - and yes I'm talking to PGMusic Support about those - but I wasn't getting them before installing Sampletank. I'm getting the feeling that Sampletank and Windows 8 64 bit just don't play nicely together.