Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
go to music store
click on account (top right hand column on the store window)
click purchase history
scroll to bottom and click on report a problem
click on the name of the track or album that has a problem
(must know exact second in the track when a problem appears when reporting a problem)

had to do this recently
took me a while to figure it out (itunes support page was no help)

best of luck

Andrew
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.