Board Thread:General Discussion/@comment-5122408-20130113024017/@comment-188432-20130113040418

It's not possible. The visual editor is not meant for the editing of "complex code", which usually includes tables. I mean, sure, you could give us a link to the page and we could tell you how to work around it. But you're just going to run into this problem again one day.

Realistically, you have two options:
 * 1) Continue to use the visual editor exclusively, accepting the fact that there will be some things on the wiki that you will never be able to edit
 * 2) Don't be afraid of source mode. It doesn't bite.  Honest.

Here's a simple guide that will help you start making tables in source mode.