[jQuery] Problem animating with marginLeft...

[jQuery] Problem animating with marginLeft...


I have this:
$('#mydiv').animate({marginLeft:100}, 500);
it works just fine in Firefox and Safari. In IE (6 and 7) I get
"Invalid argument". If I use this instead:
$('#mydiv').css({marginLeft:100});
It works in ALL browsers, including IE.
What's wrong? The comment above the animate() function even uses
marginLeft as an example