Maybe there is some user rights problem in the file system?
Could be. I'd assume that as long as your user account has read AND write access to Opera "mail" folder (and all foldres and files in it), you should be fine.
Have you messed with your HOSTS file at all? Do you have any hostnames in the file with invalid characters?> I also tried creating a second mail account within Opera
I would try the -pd switch option to rule out a corrupted profile.
If none of that helps, maybe it's a lib version issue. I think you can start Opera with a debug switch, which might give more info in the console.