I get errors just like that all the time, except usually mine say “Cannot Parse File” or something like that. The reason it imports fine is because AE doesn’t actually load all the files when you import a sequence, it just looks at the first one and then runs down the sequence to see how many images are in it – so you’ll never get an error on importing a sequence unless your first image is messed up.
Anyway, the error means that AFX can’t read the current file in the sequence that it’s trying to see… I’ve only had this problem when rendering from Maya, and it usually only happens when my render has crashed and I’ve gone back and restarted it from a current point (for example, the image sequence from 1 to 100 will open fine in fcheck and photoshop and looks fine, but realistically the crash at frame 50 prevented the frame’s full alpha from rendering, so AFX flips out on frame 50… and when I restarted my render I should have done frame 50 over again, but instead started on 51 because 50 looked fine).
I would say do a ram preview at 1/4 quality. Whatever frame the ram preview crashes at, re-render that frame of the sequence from Maya, overwriting the original one (hopefully you’re not using particles). There’s no need to re-import your sequence after that (remember from above), just scrub the playhead away and then back over that frame again… hopefully your sequence is fixed. If you have more than one instance of this, you’ll have to re-render all the bad frames obviously, but that should get you through the problem.
I hope that’s what you were asking. Best,
Ben