Can't put iTunes movie rental on iPod Touch

Hi!

Recently, i downloaded a movie on iTunes and tried to put it on my iPod Touch. It said that it was not the "primary iPod" and it wouldnt allow me to transfer it onto the iPod touch. I only have one other device and it is an old iPod nano that is incapable of playing videos.

Has anyone else had this problem and is there a way to make the iPod touch my primary device?

Thanks in advance for any help you may give me.