I have the code supplied to me for a banner ad it is a javascript that redirects through a 3rd party to the final destination.

Problem is the ad itself is loading intermittently like every 4th time in IE7 - in safari and firefox it loads every time! When it does not load the ad area is blank.

I have narrowed this down to the ad itself but cannot see anything wrong with the script.

You'll need to show us some code, or the page (preferable), otherwise there is no way for us to help you.