Thanks Charles - the problem isn't trying to go to a style at level 11. What I have is:

- a bullet style, 1-9, with each inheriting from the one lower.
- a text style, 1-9, with each inheriting from the one lower.
- for each of the above, there are actually two styles - one with no spacing after it, and one with a line's worth.

So that's 36 user-created styles I have, and no more than 9 levels of inheritance in any of them.

But when I try to create another style - based on ANYTHING, including Normal, I get the 'too many styles' error. I even get it when I try to "Update <style name> to match selection", which wouldn't result in a new style at all.