Recent virus definition updates caused AVG Antivirus to break Winamp. It'll report a virus in one of Winamp's files (a file that is actually safe). The following steps will fix the problem....

<div class='quotetop'></div><div class='quotemain'>Temporary solution (until AVG fixes their virus definitions):

1. Re-install latest version of Winamp.

2. Right-click AVG icon in lower-right corner of screen.

3. Click Open AVG User Interface.

4. Click the Tools menu, then click Advanced Settings.

5. Click Exceptions under the Resident Shield section.

6. Click Add Path.

7. Navigate to C:\Program Files\Winamp (or the path where you&#039;ve installed Winamp)

8. Click OK.

9. Click OK.

10. Run Winamp.</div>

I found it here.
http://forums.winamp.com/showthread.php?threadid=298064