Wow I'm finally back on this issue after a couple of months break :)
Thanks for your response Greg. I finally tried the solution you provided. While it didn't actually fix my problem, I did eventually resolve it in a slightly different way;
- Following the solution you sent, I was able to re-enable the 'remove instance' button.
- I clicked 'remove instance' and then restarted the CF instance.
- I then clicked 'add instance' but I got a pop-up error telling me the instance already existed. Doh!
- I then repeated the above steps but I also edited instances.xml to remove the XML node relating to the FR instance.
- After a restart I was able to re-add the FR instance in a normal way.
Thanks again for helping!
Cheers.