Hi, welcome to the forums!
Submit the file to virustotal, a multi online scanner site.
http://www.virustotal.com/xhtml/index_en.htmlIf avast is the only one detecting it, it probably is a false positve.
To prevent avast from detecting it during a scan, add the file to the exclution list. Right click the "a" icon, program settings, exclusion. Add the file. You can use the browse button.
Submit the file in a password protected zipped email to
virus@avast.com. Include the password, why you think it is a fp, which version of avast and vps that detected the file.
If it's in the chest you will have to restore it before submitting it to virustotal.
HTH