Movie Maker 2012 with Windows 8.1

I have been using this program quite happily (with a few issues re. yellow triangles/corruption despite files never being moved but I know how to fix it when it happens).

In my latest project, the initial section of the movie plays completely correctly, then after the 'split' the screen goes black - no sound, no visuals.

The timeline & thumbnails are showing correctly, and the whole project has played correctly in the recent past.

If I navigate to the videos from the 'black sections' independently & load in Media Player they run fine & are not corrupt.

All my previous versions of this project (I save regularly whilst editing) are also affected by the black screen issue at the same point in the movie.

Thanks!