"The iTunes Library file is locked..." How do I unlock it?

Question

I keep my primary iTunes library on a MacPro.
But I use a MacBook to sync my iPhone. When I do, I open the MacPro library when open iTunes on the MacBook via my WiFi network. Has always worked pretty well.
But this time, when I try to open iTunes on the MacPro, I'm getting an error message: The iTunes Libary file is locked, on a locked disk, or you do not have write permission for this file."
iTunes on the MacBook is closed, there is no dot next to the icon in the dock. So I can't close it any more than it is already.
So, is there any way to "unlock" this library so I can add a few things to it before the next time I sync my iPhone?
Thanks,
--PS

Answer 1

I had the same problem as mentioned above. 2 Users, sharing the same iTunes account. Found following solution:
Check sharing and permission for the shared iTunes folder. In my case under HD->Users->Shared->iTunes
Also check all permissions of the underlying folders and especially *iTunes Library Database file*. In my case directly in the iTunes directory
For whatever reason, that file had no sharing. I added my wife's user name with Read /Write permission and it works again.
I guess a bug in the update. It worked fine for a long time before the update.
Mark