First try a repair of avast. Add Remove programs, select 'avast! Anti-Virus,' click the Change/Remove button and scroll down to Repair, click next and follow.
Vista, win7 - Repair of avast. Control Panel, Programs & Features, uninstall a program, select 'avast! Anti-Virus,' click the Change/Remove button and scroll down to Repair, click next and follow.
You may need to reboot after the repair.
If that doesn't resolve it, the only thing I can suggest is doing a clean reinstall:
- Download the latest version of avast, 6.0.1125 http://www.avast.com/free-antivirus-download
and save it to your HDD, somewhere you can find it again (if you didn't save your last download). Use that when you reinstall.
- Download the avast! Uninstall Utility, aswClear.exe find it here
and save it to your HDD (it has uninstall tools for both 5.x and 6.0.x).
- 1. Now uninstall avast! (using add remove programs, if you can't do that start from the next step), reboot.
- 2. run the avast! Uninstall Utility from safe mode, first for 5.x if previously installed and then for 6.0, once complete reboot into normal mode.
- 3. install the latest version, reboot.