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;
}