It could be what the file does it may be considered some sort of key generator, which may be considered a trojan.
Send the sample to virus@avast.com zipped and password protected with the password in email body, a link to this topic, virustotal results, etc. might help and false positivein the subject.
Or you can also add the file to the User Files (File, Add) section of the avast chest (if it isn't already in the chest) where it can do no harm and send it from there. A copy of the file/s will remain in the original location, so you will need to take further action and can remove/rename that.
Send it from the chest (select the file, right click, email to Alwil Software). It will be uploaded (not actually emailed) to avast when the next avast auto (or manual) update is done.