We already picked this up in your support case, but for other readers, I will put the response.
This is because mocha is reading off your AE timeline and AE has run out of memory. Simply save and close mocha and open it again, that will reset the memory usage and fix the problem for you. We are currently working on a solution for this problem, but for now that's a workaround that will get you up and running.
#222222; font-family: arial, sans-serif;">If you still have trouble, it may mean you need to allocate more memory to After Effects and mocha in your AE preferences and your mocha preferences, and shut down any other programs you're running in tandem, like internet browsers, etc. You want as much memory as possible available to you so you don't have to save and close a lot. Try also clearing your AE cache between projects.