Lets wait for more advanced users to respond however keep your file
handy, you will possibly see in the source the text you entered which
you can cut and paste out into a new wiki if necessary.
This happened to me once as well, just after I modified something, or
installed a macro. I carefully searched for the thing I changed in the
source file (Using Notepad) and removed the systemConfig tag or
removed it from mainMenu so it was not loaded when I opened the Wiki.
Presto - it was fixed.
In my experience it does not occur very often.
Tony