Please, on the avast4.ini file change the value Database on section [Common] from ODBC to XML

Driver for VRDB: ODBC or XML. Mostly concerning storage and databases problems may be related to the database drivers that could be downloaded from www.microsoft.com/data.

Actually, if you need more information about the avast4.ini file you can see http://www.avast.com/forum/index.php?board=2;action=display;threadid=1647