"___" was not copied to the iPod "___" because it cannot be played on this iPod HELP?

I downloaded a video from my main computer through Zamzar.com to the format 'ipod'. After it downloaded, I moved it to my iTunes and dragged it to my iPod window and that message came up! I did this before with several other videos and it worked. What's wrong? The video is only 2 minutes long and I have plenty of space left on my iPod. I have a windows xp computer if that makes a difference. Thank you!