The file name of the video has to be "M4V#####.MP4", this is case sensitive. Replace the #'s with numbers.
Right When I plug in my PSP the file pops up and I click on MP_ROOT . Inside there is a folder named 100MNV01 I put the video that I downloaded from video.google.com which is a .MP4 file . When I check my PSP it says no videos!*I have version 2.5 on my PSP