Certain wav Files Won't Play

I assign wav files to system events.
Certain ones won't play when when I assign it to the Windows Logon event.
I previews fine and plays in Windows Media Player
I though the length was the problem 'cause these wav files are 22 and 24
seconds
but I assigned a wav file to the Windows Logon that is 30 seconds and it
plays fine.

Any ideas??
James