Recently (last week), I was told by the head coach of the football team at my school to edit the game footage into a highlight film. They laptops they have only have WLMM. When they film the game, they film it with Sony Handycams which save as .mst files. I did research before trying to edit and found out that WLMM supports .mst files. However, while I was making the highlight video for the last game, about 30 minutes into the process, 2 of the clips turned to the grey box with the yellow triangle and exclamation point. As I was going through the process of fixing those 2, others followed suit. I can tell you the files are not corrupt because they get uploaded to a website so that all the players can watch them. None of the clips ever have problems. So my question is, if the file type is supported by WLMM, and the files are not corrupt, how can this issue be solved?