After every VPS (automatic or manual) update, version in Avast’s “About” window is still old (Compilation date). That causes Windows Security Center to show up, that Avast’s VPS is out of date.
Actual VPS: 2009-07-08
VPS shown in About window: 2009-06-07
Check your system date, double click the clock and ensure the day, month and year are correct and adjust as required.
If the date is correct - 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. This has in the past resolved this out of sync issue between reported and actual VPS version.