hmm, interesting, I'm automatically logged in on this computer and I get this page: http://wiki.maemo.org/Task:PIM I am then able to edit the page. I wonder if you logged in on the main wiki page, then typed in the address if that would have you logged in on the right page.
In any case this sounds like a browser error - which one are you using, and do you have any funny settings (like no cookies, etc?)