First ensure that your system date is correct, day/month/year and adjust as required. If correct move to the next step below.
Now try a 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. This has in the past resolved this out of sync issue between reported and actual version.