inetpub error: cant find master page

I have a folder which contains all my app files, including .aspx, .htm and .master pages. I placed the folder into my inetpub\wwwroot folder, and it runs fine. But when I replace localhost with my ip address, it gives me an error.
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 '/main.master' does not exist.
It points to this
Line 1: <%@ Page Title="" Language="C#" MasterPageFile="~/main.master" AutoEventWireup="true" CodeFile="main.aspx.cs&qu ...