Invalid mailbox?

[Tony Cowell <acowell shrimpers force9 co uk>]

Hi,
I have just installed Balsa and configured my settings.
All went well, retrieved my mail from ISP and there it was in my inbox. 
Clicked it to read and balsa crashed. I now cannot start Balsa again 
because I get a error message saying Balsa has crashed.
Firstly, what files do I need to delete to go back the the first time 
use screen so I can try again?
Secondly, I think it happened because I specified a mailbox incorrectly?
Any ideas?
Many thanks
A Cowell