I have the same problem. It is grayed out in parental controls as well as shared libraries. I cannot find a way to "ungray" these options. I am an administrator account but am unable to make these changes. Have you had any luck?
I have this problem too. I removed the Radio button from the left hand column of my iTUnes some time ago. I now want to use it. But when I go to preferences the Radio select button is greyed out so I am unable to use it. What's going on?
I found out what the problem was. In the preferences there is a PArental Control option. In it the radio box was ticked. I unticked it and the radio option in the Library appeared again. Hope it works for you too!
Under general "preferences", there are a items that you want to "show". One of them is "radio". Check this box and radio will appear under "library". If this doesn't work, then look under "parental control".