Have you not thought that the only constant in this is avast which was working fine before you installed this driver.
So is it not possible that the BUG!!! lies with ATI ?
What indication have you that this is a problem with avast ?
Removing one part of any possible conflict will obviously resolve the conflict, but it doesn't identify where the problem lies. Any detailed information is more likely to be able to "correctly" identify the problem and where the fault lies.
What were the new features that were different to you previous driver, what changed, what was it that necessitated the change in driver ?
Have you checked out the ATI website, FAQs or forum (if they have one)?
If this is a bug in either ATI or avast then it is likely to be widespread as ATI video cards are popular and probably in use with other forum members.