Authorise Computer

So I can't authorise my computer as it says I already have 5 computers authorised.

I checked my Account and there are only 3 items authorised. 1 computer, 1 phone and 1 ipad. So I deactivated the ipad. The computer on there is the computer I'm trying to allow access, but it's apparently already authorised. So I deactivated it and am trying to reactivate it, but iTunes is still saying can't have more than 5 computers. Well now there is only 1 phone, that's it.

I've tried restarting iTunes, restarting my computer, running iTunes in administrator mode, but it keeps saying I can't authorise this computer because I already have 5 authorised.

Where do I go from there? Any help apprecated.