These players are very fussy when it comes to playing videos. The "file format error" messages you get when playing videos generally means the player needs the videos to be in a certain setting (w x h resolution) and frame rate. A lot of members have had success with the freeware program
viDrop so I would recommen you try it too and see how you go.
You can download viDrop from here:
Download viDrop from MyMPx.org