According to Help:Wiki navigation, the limits are:
The Wiki Navigation allows for a total of 280 links, which are grouped as:
- 4 level 1 links equally a total width of 550px
- 7 level 2 links equally a total width of 729px
- 10 level 3 links with a dynamic width (and min-width set to 150px)
The wiki-navigation is essentially a bulleted list. That means that it can be quite easy to exceed the limit of links allowed. One way to check the number of your links (as wiki sees them) is to copy the contents of your wiki-navigation to a sandbox or word processing program. Then, replace the unnumbered bullets with numbered bullets. This should make it easier to see where you actually have too many links.