The iTunes Store lets you hear short clips of music and audio books and lets you view sample clips of the music videos and movies it offers. When you play a clip or browse items in the iTunes Store, iTunes saves the data in a cache file on your computer. If you stream a lot of clips, the cache file can become large. The cache file could also cause stability problems with iTunes if the cache becomes corrupted in some way. You can reset the iTunes Store cache in a few simple steps.
Open iTunes and select "Preferences" from the "Edit" menu.
Click the "Advanced" tab and click "Reset Cache" beside "Reset iTunes Store Cache" in the bottom half of the window.
Click "OK" to close the window.