Last month, Apple shook the market with their announcement that the upgrade to OS X 10.9 Mavericks would be free, as would their suite of productivity applications: Pages, Keynote, and Numbers. Everyone likes "free", but it looks like it comes with some issues. Among the issues with Pages that have been heavily reported on Apple Forums is what appears to be a bug that prevents the inserting or editing a MathType equation. The good news is that there is a simple fix; make sure MathType is running before attempting to insert or edit an equation.
We've published an article on our website that describes the situation in more detail, and provides an acceptable solution you can use while waiting for a more permanent fix. Rather than re-publish the article here, we invite you to our website to read it.
We believe this is caused by a bug in Apple's software, thus they are in the best position to fix it. Please let them know the impact of this on you by completing their short Pages Feedback form. If you also use Keynote and Numbers, Apple has feedback forms for them as well: Keynote feedback; Numbers feedback. We are investigating the situation to see if there's anything we can do to temporarily correct the issue while waiting on fixes to these 3 apps. Meanwhile, the process described in our article can be used consistently to insert and edit MathType equations in Pages documents, Keynote presentations, and Numbers spreadsheets.