I just wanted to update everyone on the problems I was having earlier('http://www.zimbra.com/forums/showthread.php?t=5316&highlight=bad+file+descripto r') with a bad file descriptor error whenever amavis checks an incoming mail message.
The cause wound up being with perl. I had a long-ago set variable in my /etc/profile, PERLIO=stdio. This was causing the problem. Unsetting this variable allowed amavis to work without errors. In addition, Mark Martinec, one of the amavis developers, has filed a bug against perl for a similar problem.
I hope this helps someone out along the line.