A file that is moved to the chest a protected area (quarantine) can do no harm.
You don't say where you looked, if in the original location you won't find it there it has been moved.
If you used explorer to check the chest folder you won't see the original file name there either. Files are encrypted and renamed in the chest, so that you can't tell what is in the chest. It is part of the protection so there effectively can't be any interaction from outside the chest.
If you open the Chest and look in the Infected Files section, there you will see the original file name. To open the chest start the Simple User Interface, Menu (or right click on the skin) and select Virus Chest or direct access C:\Program Files\Alwil Software\Avast4\ashChest.exe (make a shortcut for quicker access).
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You should 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, 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, see
http://forum.avast.com/index.php?topic=34950.msg293451#msg293451, how to report it to avast! and what to do to exclude them until the problem is corrected.