Board Thread:Support Requests - Designing Your Wiki/@comment-1450483-20130331210442/@comment-4674838-20130331235729

As explained on the help page I linked, you can only have a maximum of 5 level 1 links. One of those 5 is the "On the Wiki" that's always there, so you can only have 4 of your own.

You will need to make sure to not use more than 5 level 1 links, and make sure the titles are short enough so that there's no overflow (make the titles shorter if necessary). That's what it means by "menu is too wide".