HEllo there , im having a problem with some movieclips .
Im Working with very old files and when i open them in the latest Animate, some of my Moviclips that have images (pngs) inside, apears to be RED - seems like it replaces de original image with a RED Rectangle.
If so and if this is an incompatibility issue, the best you can do is to open up these files in Flash CS6 - which is the last one from the Flash era -, save and then try to open them up in Animate.
Another possibility is that these red rectangles are simple masks. If so, you can just delete them.