I'm sure this is an implementation issue. Here's the quick code you might want to double check with:
Code in Master Page:
<head runat="server">
<title>Testing Page</title>
<link rel="stylesheet" href="StyleSheet.css" type="text/css" />
</head>
The CSS Code:
body
{
background-color:Red;
}
If you want to use the Pages Directive you should have a Theme build and then you can use:
<
pages styleSheetTheme="Theme1"></pages>
Assuming that App_Theme folder of your web Application contains a Theme1 folder which holds the CSS.
I've personally used both apporaches in past and they've worked fine. So, I am thinking there might be something wrong with the code...
If you post your code here others / I might be able to take a look at it and help you.
Cheers,
Me.