The Error Page is a page that appears when an error has occurred, like a deleted page, user or unexisting page on the website.
The Old Design showed a Noob "walking" a TNT-Like brick, which existed from 2007-2012.
The next one shows a white isosceles triangle with yellow outer lines with an exclamation point inside it. Existed from 2012-early 2014
The new one is Builderman falling to a hole which is currently being used.