Maybe your photoshop is set to CMYK? Or to 24-bit instead of 32, or viceversa. Have you tried throwing them into MSPAINT, saving as BMP and then importing?
We have plugins for max9 and up (32-bit and 64-bit flavors). Should there be significant interest in support for earlier versions we will take it into consideration.
Congrats to polycounter Charles for the GamesRadar writeup! http://www.gamesradar.com/32-bit-graphics-are-new-retro/?utm_source=dlvr.it&utm_medium=facebook