It may be that a newly added signature happens to match a string on the file.
You could also check the offending/suspect file at:
VirusTotal - Multi engine on-line virus scanner and report the findings here. I feel virustotal is the better option as it uses the windows version of avast (more packers supported) and there are currently over 30 different scanners.
Create a folder called Suspect in the C:\ drive, e.g. C:\Suspect. Now exclude that folder in the Standard Shield, Customize, Advanced, Add, type (or copy and paste) C:\Suspect\* That will stop the standard shield scanning any file you put in that folder. You should now be able to export any file in the chest to this folder and upload it to VirusTotal without avast alerting.
If it is indeed a false positive, add it to the exclusions lists:
Standard Shield, Customize, Advanced, Add and
Program Settings, Exclusions Restore it to its original location, periodically check it (scan it in the chest), there should still be a copy in the chest even though you restored it to the original location. When it is no longer detected then you can also remove it from the Standard Shield and Program Settings, exclusions.
Send the sample to
virus@avast.com zipped and password protected with the password in email body, a link to this topic might help and false positive in the subject.
Or you can send it from the chest (select the file, right click, email to Alwil Software). No need to zip and PW protect when the sample is sent from chest. A copy of the file/s will remain in the original location, so any further action you take can remove that.
