Hey guys,
Just a note on this method.
All I deleted was the 'ext' file, leaving from the dungeon to the moat in the south-east corner.
Can now enter/exit the castle without issues.
Cheers this works great, also If you don't want to redo all the areas I think you only need to delete the area that you can't access:
Int_02 - Top Floor with the clerics
Int_01 - Main floor where Raedric is.
Int_03 - Dungeon
Ext - Outside