Upload the file to Virus Total at https://www.virustotal.com/
on the web. Virus Total will scan it in a couple of minutes with 50+ antivirus programs, including the Clam AV scan engine used by ClamWin. If only 1 or 2 other AVs besides Clam AV say it is infected, it is most likely a false positive. I like to see at least 2 of these AVs detect a file as infected before I believe it: Avira, Bitdefender, Eset (Nod32), Kaspersky, and Sophos. They all use their own scan engine and have a wide user base which includes lots of businesses, which tend to use the better AVs.
Virus Total will send a copy of false positive files to the AVs that falsely detect it so they can correct their virus signatures. but you might speed up things a bit if you also submit it to Clam AV at http://www.clamav.net/reports/fp
on the web. It may take Clam AV a week or so to correct their signature because no one works on Clam AV full-time--they have other duties for Cisco (the owner of Clam AV now). You could whitelist the file in ClamWin's tools if you want to.
Thanks for using ClamWin!