B4 setContent('html' issue ....

Alex
I am getting an alert (only in IE) on: AW.System.HTML
over the block:
if(split) {
    var ref=this.getContent(split[1]);
    return ref.getContent(split[2])
}  What I am doing is replace full div-container with a set of buttons
seems that replacing the same area where the button clicked is with a new button is causing this alert (as a similar one without replacing same area worked as expected);
the line causing it looks like:
TBar.setContent('html', TBar.getContent('html') + eval('Btn' + i) );  If you want, I can send you the full code.
This had no problems under B3 (IE or FF)
Thanks

I forgot to say that the alert says 'undefined' :
(and of course there is a previous line in my code without the '+')
TIA