Zune trouble

[xkylex14]

So...i download a video (it was a .avi) so i converted it to .mp4 using media coder, and i put it in my zune folder and when i plug in my zune to sync it wont sync to my zune. Then, I took a video that was already on my zune and removed it from the folder and synced my zune and it removed from my zune. Then i dragged the same file back into the folder and synced it again and it wouldn't go back on the zune. I don't understand why it wont sync to my zune if its in the right format. So, if anyone knows how i can fix this problem please help.