.mp4 videos cannot drag to phone in itunes

[Alpdog14]

I recently got a iphone 4 for xmas and trying to figure out how to put a video on my phone. I have itunes installed, and the video was in .avi format, I then proceeded to download and install Handbrake which I read will convert it into the .mp4 format. I converted the video into mp4 format and added it to my library but when I try to drag the video from my library to my phone "Movies" folder all I get is that circle with the line through it (no smoking sign) saying I cannot do it. I also tried then to convert to a .m4v but that does not work either. Does anyone know what I am doing wrong? the converted videos play fine on my PC and in itunes and not sure what I am doing wrong. I have also tried to create a new playlist which I am able to add the video to on itunes but when I sync my phone nothing gets copied over so not sure what I am suppose to do. Any help would be most appreciated .

What even stranger, is I just tried to just transfer a simple .mp3 into my Music folder and I cannot do this either. Does anyone know why this could be happening, I have authorized this computer already but it seems I cannot seem to transfer anything to my phone.

Ok I just spoke with my co-worker who has a iphone and she mentioned that I can only sync on one computer. Which is why I cannot put anything on my iphone from my work computer because I already created the sync on my home computer, is this true??? has apple not fixed this problem where you can have multiple sync locations? Please let me know if this is true, that I can only sync on my home computer.