Can't load addons on cata or mop servers

As title suggests I can't load addons on Frostwolf or Nelth. On the load screen I don't have a addons button and ACP doesn't load so I can't access addons in-game. There is no problem on Icecrown. This is the first time this has occurred in all my WoW history. Does anyone know what might be going on?

are you using the same Addon version for Wotlk? You need to download the correct version for Cata/MoP in case

Nope, but I just resolved problem by unchecking read-only on the wow folder (and subs) and then running wow.exe as admin. Problem solved thanks!