bit of a long story so let me try and explain what I have done...
I have the app (Version 1.0.2) installed on WordPress (3.4.1) and it was working fine. I could create a post and it would publish to the specified fan page.
I then noticed that it also published to my personal Timeline and I wasn't happy with the wording as I had given it a poorly worded Display Name and I therefore wanted to change it.
Instead of what I now assume would have been the easy option of just changing the Display Name, I went into my FB Account Settings -> Apps and removed the app from the list of authorised apps.
I then deleted the app from developers.facebook.com, created a new one with the correct Display name and sensible Namespace and configured the WordPress plugin settings but whatever I do I can't get the app to request permissions on my FB account and therefore the "Publish to fan page" option is showing as disabled.
Any and all advice is appreciated,