Fatal error with cms_content_tree::getRootNode()

[appleyard]

Recently upgraded an installation of CMSMS to 1.9.2. Noticed that the {sitemap} tag wasn't working anymore so switched to {site_mapper}. Now the page gives this error:

Fatal error: Call to undefined method cms_content_tree::getRootNode() in /[my server path]/modules/MenuManager/action.default.php on line 135

I tried replacing with a regular {menu show_all="true"} and it gives the same error. Oddly, I'm using Menu Manager elsewhere in the site with no problem.

Does anyone have a clue what could be going on here?

[Dr.CSS]

Did you go to Module Manager after upgrading to check if any extra/3rd party module may need to be upgraded?...

[appleyard]

Yes. TinyMCE and FormBuilder are still on older versions, but I can't see how those would cause this, especially since I've disabled WYSIWYG editors. (And when I try to upgrade FormBuilder via Module Manager, it gives me a fatal error related to nusoap memory exhaustion, which sounds like a whole 'nother issue.)