Left offset

Hi NG

I have created a fairly simple dynamic drop-down menu, which works by
hiding/showing DIV's (in another frame, though) on mouseover. I have
built the menu so that it can cope with left/right scrolling, i.e. the
DIV's always turn up in the same place, relative to the rest of the
page content. I am calculating/measuring the left offset in order to
this. So far, so good. My question is now this:

Sometimes (rarely, actually), I get an "Object does not support this
property..."-error on this code line, in which I determine the amount
of left/right scroll:

var ScrollLeftOffset = parent.main.document.body.scrollLeft;

What is wrong, and why doesen't the error occur everytime I use the
menu, but only perhaps 1 of every 50 times? Is there another, more
stable, way of determining the left offset?

Hope somone can help me out.

Thanks!

regards,

M.L.