When updating the PROGRAM, and when there are problems updating the database right after booting, some glitch in the detection of your current database version might occur.
If the problems are just a one time thing, then rebooting again usually solves the desynchronization issue.
If rebooting again (or even twice) doesn't solve the problem, post back with details about your OS, Avast edition and version, firewall, other security tools (past and/or present)...