2

What Operating System are you using ?

Trojans generally can’t be repaired (either by the VRDB or avast virus cleaner), because the entire content of the file is malware, so it is either move to chest or delete, move to the chest being the best option (first do no harm). When a file is in the chest it can’t do any harm and you can investigate the infected warning.

The VRDB only protects certain files, .exe, dll and other system files, it doesn’t protect data files or all files, it is not a back-up program, so there are going to be many occasions where repair won’t be an option.

Only true virus infection can be repaired, e.g. when a virus infects a file it adds a small part to it, provided that file is one that avast’s VRDB would monitor and you have run the VRDB, then it may be possible to repair the file to its uninfected state.
However, for the most part so called viruses, trojans (adware/spyware/malware, etc.) can’t be repaired because the complete content of the file is malicious.

It may have the same name as a system file (a common tactic), but the location may be incorrect, in windows XP mine is in C:\windows\system32\svchost.exe and C:\windows\ServicePackFiles\i386\svchost.exe.

You could also check the offending/suspect file at: VirusTotal - Multi engine on-line virus scanner I feel virustotal is the better option as it uses the windows version of avast (more packers supported) and there are currently 32 different scanners.
Or Jotti - Multi engine on-line virus scanner if any other scanners here detect them it is less likely to be a false positive. Whichever scanner you use, you can’t do this with the file in the chest, you will need to move it out.