I just ran into the problem that I added a WebPart to my SharePoint page that causes an error. With this error I'm not able to remove the WebPart from the page because I cannot access the administration page.
I found some working hints in Coskun Cavusoglu's blog.
So just add ?contents=1 to your url and you'll be redirected to the managing mode of the page. Another way would be to call /_layouts/spcontnt.aspx?&url=[relative url to the page with errors].