I have several TIFF sequences (with alphas) that are giving me a headache. When I import them into AE, I get an "AEGP Plugin TIFFIO: Failed to open the file" error.
I researched the forums and found that this could be related to odd formatting of the source media (my TIFF sequence). I created these TIFFs in Maya 2008 and I have imported other sequences made with Maya into AE with no issues.
Just to be sure, I created a Photoshop droplet that re-saved my TIFFs as Photoshop TIFFs with the same names.
I re-imported the new Photoshop TIFF sequences (still with alphas) into AE CS3, and I get the same error.