After removing iTunes version 11.0.0.163, and reinstalling version 10.7.0.21, I found that when I tried to run iTunes again I got the message "the file iTunes Library.itl cannot be read because it was created by a newer version of iTunes".
I found the answer to this problem on the Microsoft Windows Community forum page(http:/answers.microsoft.com/en-us/windows/forum).
"iTunes cannot be launched because the library file was modified to work with the newer iTunes version, so is no longer compatible with the previous version. But Apple does backup the iTunes library file into a subdirectory that you can use to go revert back to the previous version".
There then follows the procedure to use.
If you type the message as I quoted above into your browser, (Google or whatever), the Microsoft entry should show up in the list.
Of course you need to be running Windows for this to be of any use to you, also it won't work if the Library file has been altered in any way.
It worked for me, hope that this might be of some help to you.