help with psp video playback

when I try to play any Mp4 or Avc video I convert for the psp I get the message "Video Can't Be Played" I have used two different converters including psp video 9. My firmware is 3.40 OE-A

are you placing both the .mp4 and .thm files in its appropriate folder?

and the appropriate location to place to .mp4 and .thm is in the VIDEO folder on the root of your memory stick pro duo.

that was problem, by the way what do I do if Xvid4psp won't mux the audio and vedio at the end of conversion