Opera Issue

[Obi1-Cannabis]

hi, i have 2 div's with the following styles:

.ppup2{	width: 80%;	background-color: #FFF;	border: solid 1px;	position: fixed;	_position: absolute;	_top: expression(eval(document.body.scrollTop));	left: 10%;	padding: 0.5cm;	font-weight: 900;	filter: alpha(Opacity=90, FinishOpacity=90, Style=2);	z-index: 3;}.bloqueador{	width: 100%;	height: 100%;	position: fixed;	left: 0%;	top: 0%;	_position: absolute;	_top: expression(eval(document.body.scrollTop));	background-color: #000000;	filter: alpha(Opacity=30, FinishOpacity=30, Style=2);	opacity: 0.4;	z-index: 2;}

the first is to display an error message after a javascript form validation (if that's the case) and it's working fine in ie7 ff and opera. The second one is to use in front of the web-site content so that the user can't do anything until he presses 'ok' in the first div and it's working fine in ie and ff and almost in opera, the problem here is that the div doesn't stay fixed it simplay stays static in opera.can anyone think of somethink to resolve this?