You might have tried running your saved clips from IV:MP using the Video Editor, and probably ended up crashing. I don't know whats causing the issue but I do have a solution for you.
- Select any server and join it.
- Press esc, go to the game tab and load your single player saved game.
- Once you are in the game, open the video editor like you normally do, with your in game cellphone.
- The video editor should work just fine.
I assume the devs are aware of this issue and working on a fix.
Thanks to Vittorio for actually trying to find out the solution.