Just the same as with another recently posted topic, this is a frequent EP development helper / time saver and always have to go to my cheat sheet to recall this. Say you just added a user control on a page and, due to some issues with it, the page stops to render itself properly, but even worse, you just can't get on it to fix the issue.
So, to fix this, open your page and append to the URL the following: ?Contents=1. This will open a page with a contents' items list, so you can just select the last added (offending) user control and delete it.
Now you will be able to navigate to the page again.