What is the infected/suspect file name, where was it found e.g. (C:\windows\system32\infected-file-name.xxx) ? Check the avast! Log Viewer (right click the avast icon), Warning section, this contains information on all avast detections.
The file name and location might give an indication of why it might have been detected, in the past some virus signature files have been detected, but without information we won't be able to say one way or another.
If he no longer has counterspy, the uninstall routine should have removed the folders (?) at least I would have thought so.
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.