I got this error while working with web app. This is my master page
<head runat="server">
<link href="Styles/Site.css" rel="stylesheet" type="text/css" />
<asp:ContentPlaceHolder ID="head" runat="server">
</asp:ContentPlaceHolder>
</head>
This is the error:
Error: The stylesheet http://localhost:55381/Login.aspx?ReturnUrl=%2fStyles%2fSite.css was not loaded because its MIME type, "text/html", is not "text/css".
Source File: http://localhost:55381/Login.aspx
Line: 0
Try this:
<location path="~/Styles">
<system.web>
<authorization>
<allow users="*"/>
</authorization>
</system.web>
Where Styles is the folder that contains style sheet. I solved it this way