Don't forget spcontnt is your key for 'web part' error resolution
(This articles has already been posted in www.msd2d.com. Now I post it again in my own blog.)
Eventough webpart is very powerfull, but debuging web part is painfull. For example, you forget to put try-catch block in your code - and one day you get error without any clue to edit. Or imagine, you’re creating on-the-fly graph web part, and send wrong HTML header to the page. Causing Sharepoint page shows image only and no interface to access.
What should we do ?
Remember that Sharepoint has spcontnt.aspx - an interface to edit web farm content,
Change [YOURSITES] to url of your site, and [FULLYENCODED_WEBFARMPAGE] to url to your web farm.aspx page.
Then, close the offending web part.