Can no longer open a page in the backend after changing its master page
After changing the master page of one of my pages, I all of the sudden get a "Cannot unregister UpdatePanel with ID '' since it was not registered with the ScriptManager" error and no longer can open a page of mine on the admin side (on the public side it works just fine). The Change Template option no longer shows up for it and I don't want to delete the page and thus lose my work on it.
How can I fix this without deleting my page? Like I said above, it no longer shows the Change Template option (It only shows Change Owner now) so I can't just change it back to the template it used before. Another thing to note is that I am not using any update panels or doing any AJAX of my own. All that is on the page (that gives that error on the admin side) is a contact form and a content block.
I am using the latest version of Sitefinity with the hotfix.
Update: I found that I can revert to an older version of the page, but if I again change its master page, i get the same error again when I attempt to open the page for edit. Also, it looks like I can not access the admin view of any pages that use this template page (which is the child of another template page). This troublesome template page inherits from the parent template and only adds a shopping cart summary and nothing else.