Delete Error Web Parts from Edit/New page

First navigate to the page that has the problematic web part. Then at the end of the url add the url parameter Contents=1. This will open the page in 'Maintenance' mode.

Now all the web parts can be viewed, even those with errors.

Users can select and delete the required web part the page will work as expected.

Example Problematic Url: 

http://yoursharepointsite/Lists/ComboBoxTestList/AllItems.aspx

With Url Parameter:

http://yoursharepointsite/Lists/ComboBoxTestList/AllItems.aspx?Contents=1