The tiff is probably not RGB. Open it up in Photoshop and check the color space. AE only works with RGB or RGBA images. I'll bet that you'll find it's CMYK color. It could even be Lab color. Change it to RGB and everything will be fine.
What Rick said. There are over 200 sub-formats for TIFF ranging from 2 color fax to 32bpc floating space and any number of combinations of compression settings and arbitrary data such as "layers". Open it in PS or an image viewer, save it as plain 8bit/ 16bit RGB from there uncompressed or using LZW compression only. That's what AE likes.