Tiny MCE Image image upload functionality has stopped working

I was working on a MODX Revo site (2.2.6-pl) when the image upload functionality for TinyMCE stopped working. When trying to upload an image into the Content area, the ability to upload images has disappeared as well as all the directories in the images container. Not sure where the error is occurring. Here's a quick screencast explaining the problem:

http://screencast.com/t/RSmzRdaR0

I tried removing Tiny MCE and re-installing it, but this does not help either.

Anyone else run into this issue?