Because I believe you are excluding it from on-demand scans, avast Settings, Exclusions and it is being detected by the File System Shield, Expert settings, Exclusions.
Excluding the whole folder is leaving a hole in your security, you should change the \* at the end of the path to \file_name.exe of the executable file.
You could also check the offending/suspect file at:
VirusTotal - Multi engine on-line virus scanner and
report the findings here the URL in the Address bar of the VT results page. You can't do this with the file securely in the chest, you need to extract it to a temporary (not original) location first, see below.
Create a folder called
Suspect in the
C:\ drive. Now exclude that folder in the
File System Shield, Expert Settings, Exclusions, Add, type (or copy and paste)
C:\Suspect\* That will stop the File System Shield scanning any file you put in that folder.