Good to hear you got it fixed. A common reason for this issue is a problem with security permissions. This is another approach that may help in such cases.
Right-click on your main iTunes folder and click Properties, then go to the Securitytab and click Advanced. Use the Change Permissions... button grant to your account (or the Users group) and SYSTEM full control of this folder, subfolders and files, then tick the option to Replace permissions entries... which will repair permissions throughout the library. When complete switch to the General tab, click in the Read-only check box to clear it, then click Apply.
If you don't have the option to change the permissions then use the Owner tab and Edit... button to take ownership from an account with administrator privileges. Tick the option to Replace owner on subcontainers and objects.
Repeat with the media folder if it isn't stored inside the main iTunes folder.