Hey there, Jon–welcome back to the forums. 🙂
Sorry you’re hitting some trouble with creating posts after the update to 3.9.1. Let’s see if we can figure out what’s going on here.
First off, are your running 3.9.1 for both The Events Calendar and The Events Calendar PRO? Make sure they’re both updated and running the same version.
Secondly, do you still see the issue if you switch to a default WordPress theme? Please try activating Twenty Fourteen to see if the issue is still present.
Next, I see that you noted trying to deactivate all other plugins. Did you notice a difference under those conditions? How about when you deactivate all other plugins with the default Twenty Fourteen theme activated?
Lastly, if the issue is still there, does the issue go away if you revert back to 3.9 for both plugins?
Please give those steps a shot and let me know what you find.
Cheers!
Geoff