Indiana Jones 4: Screenwriter Frank Darabont recently attended the Santa Barbara film festival where he spoke briefly about why the Indiana Jones 4 script and the reason it has not been greenlit yet. Ain't It Cool has the transcription from the event...

"The short and simple version of the Indiana Jones 4 situation is that after more than a year of working closely with Steven Spielberg developing the story, I had completed a screenplay that Steven loved and was hoping to shoot in July of this year. However, George Lucas had issues with the script and slammed on the brakes in order to rework the material himself. There is talk of enlisting another writer. Given that George is the producer, but even moreso because of their long and close friendship, Steven is deferring to George in this situation.

It is now up to them to try to find a common ground regarding the film. I wish them luck and hope their efforts result in something they're both excited about shooting. What, if anything, might remain of my work at the end of the process is anybody's guess, assuming the film even gets made at this point. As for me, I'm disappointed, but I'm putting the experience behind me and moving on with my life and my own projects."