1. What other security software do you have on your machine?
2. What is your OS, 32 or 64-bit?
3. What version of Avast are you using? 5.0.594 is the latest one.
4. What product of Avast are you using? Free, Pro, or AIS?
5. Are you current with your Avast updates?
6. Did you run any scans to see if you have malware?