I just added a web part to a page and it seems that it didn’t agree with SharePoint 2013.
The worst part of it is that this was the home page of this particular site. Normally you could just delete the page and re-do it, but I thought there must be a way to remove the faulty web part without doing that. Alas, there is, thanks to Nothing But SharePoint & Mai Omar Desouki.
So the error i got kept saying “Object not set to an instance of an object” as soon as you click on the page. To solve this add this to the URL: ?Contents=1
It will show you a list of the web parts on that page, which you can then go ahead and delete the one that is faulty.
Thanks again to Nothing But SharePoint for this great post.