Transparency problem in IE7 with Hover

[beary]

Hi,

I've googled for this answer but I don't think I know the right search phrase to type...

I have a fairly simple hover effect. When the user mouses over a link, a box appears with extra info. This works for all browsers. However, in IE7 only, it's as if the transparency is set to 60%. In other words, I can still see the text which is present without hovering. In FF, Safari, Chrome etc, it's totally blocked out when I hover.

Is there some way of completing blocking it out in IE7? I've put the style listing below.

Thanks

span.hovercal {position: fixed;}
span.hovercal a span { 	display: none;}
span.hovercal a:hover { 		color: blue;	text-decoration:none;}
span.hovercal a:hover span { 
    display: block; 
    	position: fixed; 
    	left:10px;
    	top:250px;
    	margin-top: 5px; 
    	margin-left: 5px; 
	    width: 400px; 
	    height:300px;
	    padding: 5px; 
    	z-index: 100; 
    	color: #fff; 
    	background: #90c; 
    	text-decoration:none;
		cursor:default;
		text-align:left;
}