Probably a case of the broadcasting tower changing as you move around, the server sees it as you logging off from one computer and logging in with another. You'd probably want to request a session timeout exemption to prevent that. I think, anyway.
I've tried SWC from a couple of different phone browsers, and had no trouble. I haven't tried a blackberry, I must admit. I did also have trouble a couple of times based on location (not sure what that was about, unless I was right on a tower border like Ellias says), so you might try logging in from somewhere different than normal, if you've only tried it from one place.
"May the Grace of Ara go with you, and His Vengeance be wrought upon your enemies."