Editing "Send Mail As" feature is broken

Editing "Send Mail As" feature is broken

I want to change the name that I send email as when using the web interface. In the mail Settings, under "Access old version for" there is a " Send Mail As" option. This takes me to the old version. If I click on the edit icon for an email address, nothing happens. In the developer console an error is reported: "SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data" along with a network response with an HTTP 500 internal server error code.

What can I do to change my "Send Mail As" name?