If you are sure you entered the correct password and are still having difficulties, you may try an Avast Repair:
XP Users:
- Go to Control Panel > Add/Remove programs > Avast Antivirus.
- Scroll down and choose Repair function in the pop-up window.
- Reboot.
Vista & Win7 Users:
- Control Panel
- Programs & Features
- Uninstall a Program > Select Avast Antivirus
- Click the Change/Remove button and scroll down to Repair
- Click Next and follow.
- Reboot.
If the Avast Repair fails to fix your problem, your only other option is to uninstall Avast and do a clean install with no password. If you decide to use a password again, please write it down and keep it in a safe area. Thank you.