I just changed Avira Antivirus (in another machine) to Avast. I then noticed that while using Explore Image feature from Acronis True Image (v7.0 build 638) the computer hangs and become completely unresponsive needing a (cold) reboot. There is no problem with image files (verified) so I thought it might be the antivirus exchange. I removed Avast and reinstalled Avira and voilà, Acronis became fully functional again. Turning off active shields didn’t help at all, most likely because the culprit may be an Avast service.
Did you removed Avira completely before installing avast ?
http://www.ache.nl/index.php?location=mal-01