Changing inbox directory error

[Hirada Batanguena <pinguinpunk gmx net>]

I do get an "unknwown error 4294967295" as soon as I try to change my Inbox 
Directory. Since Mail Retrieving did not work (it just pops up  a small 
window and closes imideately) I changed my mailbox to 
/var/spool/mail/tuxpunk. Just to see if/what would happen). This resulted in 
a "this is not a mailbox" error. I have of course created the dir before.
No problem, but I can not switch back to /home/tuxpunk/mail (what was the 
original setting) due to above error. It works fine for "local mail" 
(settings/mail server), but not for  the inbox properties.