Error message div is pushing out content in other divs

Only happening in ie not moz

[snowbunny]

In my login page, the layout is as follows:
Main header bar across the whole page, then a three column layout with a left toolbar, central welcome message and right toolbar, where the user logs in. When a user logs in incorrectly, an error is displayed above the login box in the right toolbar, which pushes the content in that column down. This is fine in Moz. In ie, the error message's appearance pushes the content in the the welcome message div down too. Any ideas why this would be happening and how to stop it?

[snowbunny]

Actually I managed to work out a fix using the xsl logic to determine whether an error message is being called, and asking it to call a different div, which is has different margins in ie in the css. This isn't a pure fix, but it's a working solution. I'd still like to know what was causing it....