Wait, wait,
Before you erase the file or anything, did you check if the file was complete when you listened to it in iTunes?
I once tried to download [A good film] and it got at like 99% and alla of a sudden it restarted by itself from scratch. I went to the Incompletes folder tocheck it out and found that the file was complete (well, it was radically corrupted so I didn't keep it).

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iMac G4 OSX 10.3.9
RAM 256MB
LW 4.10.5 Basic
ADSL anything from 3 to 8Mbps/around 1024kbps

"Raise your can of Beer on high
And seal your fate forever
Our best years have passed us by
The Golden Age Of Leather"
-Blue Öyster Cult-