The vrdb generates a database with important systems files. Depending on your settings it does this when the system is idle or when the screensaver runs. As soon as the files are in the vrdb, Avast is capable of putting the original files back when a system file is infected. Since you just installed Avast, the vrdb didn't had the change to generate the database, so it can't put the original file(s) back. Therefor you need to solve it in another way. Please tell us what file(s) are infected, where they are located and with what virus. Also mention the version of Avast you are using and the version of the vps.