So to try to figure out what isn't wrong rather than what is...
I created a simple MasterPage:
<%
@ Master Language="VB" CodeFile="Default2.master.vb" Inherits="Default2" %>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<div style="background-color: #c0c0c0; padding: 40px;"> </div>
<div style="padding: 10px;">
<asp:contentplaceholder id="Main" runat="server" />
</div>
<div style="background-color: #c0c0c0; padding: 40px;"> </div>
</div>
</form>
</body>
</html>
And changed the code i posted last post to use "Default2.master" instead of "Default.master" (which again, is the master page from PWS)...
And..... the calendar works as it should! (grrr, this is becoming as clear as mud !)
So the problem is not using MasterPages itself, it's something inside the Default.Master code/design/outputted HTML..... I don't even know where to start to try to find out what the hold up is