Itunes library issue, its locked?

I apologize in advance if someone has already asked this question but i cant seem to find an answer in the support section of this site.

Ok here it goes. When i try to open itunes a message pops up saying that the itunes library.itl is locked on a locked disk, or i dont have the write permission for the file. This also seems to be a user specific issue since my sister can access Itunes fine from her account.

Were both computer administrators
I have the most recent itunes updates installed


Any help would be greatly appreciated.
Thank you.