Media Pending problem in Adobe Premiere CS4 (video preview after render)

I had this problem with 'media pending' yellow/green screen after rendering anything in the timeline.

The problem was eventually discovered when I removed the /3GB and /PAE switches from boot.ini (that I had recently added myself after installing more RAM).

Adding these switches (I don't know if it is one of them or both), will cause your video preview after rendering most types of media to stop working.

Hope this helps anyone else because this solution was nowhere to be found on the internet.