Two options. First try opening the project with the Caps Lock key on.
If that doesn't work, try opening AE and then import the project with the caps lock key on.
Then open up the comps and start turning off effects. When they are all off, release the caps lock key and start turning the effects back on one at a time. You'll find what's causing the problem.
I tried both and still got the same error. So you think it has to do with one on my effects? I have a couple 3rd party effects installed, 1 on which is being used on this project.
- trash the AE prefs
- flush the disk and media cache
IIRC, these kinds of errors are not about effects, they're related to media files. You may have lost one, you may have corrupted one, something may have changed to CMYK from RGB.