Yes mine also does 'Immediate crash&quit when trying to go into offline mode' I simply leave it in on-line mode, it tells me it is unable to connect to the server, I press OK and then carry on.
I'll just point out, I only use Windows Mail as a newsreader.
There are two "methods" for "offline mode": do not have a network connection and be forced to the dialogue – or manually select "offline mode" over the file-menue. In both there is an immediate crash&quit as soon as offline mode is confirmed (in the dialogue or when selecting it from the menue) – independently whether the program was still on in online-mode and manually put into offline mode or network connection got lost – or started without network connection. The only solution here is to have any kind of local network connection to keep the program running without internet.
How do you keep it "on"? What "OK" are you pressing?
Btw: same problem with windows 8
- Windows 8.1