Red frames in preview and render

Hey, I'm directing a huge youtube project in which we're releasing a video every single week. So this is a massive inconvenience. I'm getting red frames in the previews and red frames upon export. I've read a lot about this problem in Premiere Pro but there doesn't seem to be a workaround in Elements. I've tried deleting my media cache but it doesn't make any difference.

I need this problem fixed as soon as possible, it's making editing extremely difficult, since I can only do certain videos (some mp4s work fine, others only do the red frame nonsense and I have no idea why).

Please help!