Get "blur" when zooming in

When taking a movie and I zoom all the way in with my Canon S5IS (digital zoom is disabled) I get blur and lose focus. Any suggestions?

thanks...

HOSTED PHOTO
please log in to view hosted photos in full size.

Are you shooting in low light locations? Could be the camera dropping the shutter speed to accommodate low light. I'm not too familiar with that specific camera but that's the first thought that came to mind re: blur. Focus is still a mystery to me though

I was doing portraits yesterday and found my 70-200 blurring----- it was definitely due to lighting. My main light burnt out and I was using strobes-- had a hard time trying to work around it --- but in the end it worked for me.

are you maybe to close to the subject for the amount of zoom you are zoomed into

have you tried using manual focus?

Depends. I have not used your camera. But others I have used had this problem. Its related to the camera doing zoom but not focus at the same time. So when you stop zooming does it focus. Also you said that you focused in to the limit. Maybe you are to close for focus.