Hi All

I've been encountering some bizzare behaviour from Emacs occasionally.

I'll be writing a program and all of a sudden the Tab key stops working. 
Emacs stops automatically indenting and nothing happens when I press Tab to 
manually indent. I end up having to copy a previous tab space and paste 
whenever I want a tab (quite often).

Any idea what could be causing this? It's a buffer specific problem - if I 
open another buffer it works fine.

TIA
David