Could also be hard disk trouble, or just bad tracks having been put on the player. You also didn't say which software version you were running, at the moment only 2.0 final is known to be completely stable.

Make sure you're running software version 2.0 final, Make sure you're not running any third-party applications, remove reservecache from your config.ini if it's there, do a RAM test, check to see if it's a bad track, then check for hard disk trouble.