I'm new to Windows Movie Maker.  I had loaded a very long (2 hours) HD video (mp4 format) and was splitting it up into clips.  It was working fine, until I got to a point where I tried to split a clip and nothing happened.  The button was enabled, but there was no effect.  If I tried to do it again, it would remove all of the clips from the project and just show a black screen.

I was able to save my project with the clips, but if I reopen it I just have the same error.  If I delete all of the clips except the last one, I am able to save the last one as an mp4 successfully.  If I try to delete all of the clips except for the first one, the software crashes.  If I just delete the last clip, then the next-to-last clip becomes the problem, and partway through the clip playback stops working.

I can start over but I'd like to know what's going on so I can avoid getting stuck in this situation again.  (I'm on windows 10, using whatever version of movie maker came with it in windows essentials.)