You got a worm in one of your downloads. Try this fix first:

http://www.gnutellaforums.com/showpo...&postcount=141

If it doesn't work then try step 5 here:

http://www.gnutellaforums.com/showthread.php?t=41432

Even if the first link fixes your problem, you should read a bit more about how to steer clear of bad downloads in that thread. Maybe look at this one as well:

http://www.gnutellaforums.com/showthread.php?t=58603