Server Error in '/' Application.

Parser Error
Description: An error occurred during the parsing of a resource required to service this request. Please review the following specific parse error details and modify your source file appropriately.
Parser Error Message: The file '/MainPage.master' does not exist.
Source Error:
Line 1: <%@ Page Language="C#" MasterPageFile="~/MainPage.master" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" Title="Untitled Page" %>
Line 2: <asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
Line 3: <div class="page">
Source File: /Default.aspx Line: 1
Version Information: Microsoft .NET Framework Version:2.0.50727.1891; ASP.NET Version:2.0.50727.1433