I obtained a 1G RS-MMC card today and loaded a bunch of .mp4 videos that I had converted earlier that plays on the Ipod and PSP. Unfortunately I cannot even open these files from the Video player on the 770, and trying to open the files from the File Manager, gives me "Unsupported file type"

According the the FAQ, the 770 should support:

Audio: MP3, Real Audio, MPEG4, AAC, WAV, AMR, MP2
Images: JPEG, GIF, BMP, TIFF, PNG, Animated GIF format, SVG-tiny, ICO
Video: MPEG1, MPEG4, Real Video, H.263, AVI and 3GP

What gives?
Thanks in advance for your help.