[Tootech]

Hi Jazz,

I'd be temped to run a System Restore to yesterday or day before - maybe the quickest and easiest solution.

Failing that, have a look here for two different fixes - the second link is the official Apple fix.

WikiAnswers - How do I fix this issue ITunes Library itl file is locked on a locked disk or you do not have write permission for this file

iTunes for Windows XP: "Disk is locked" or "iTunes folder cannot be found" when installing or opening iTunes