Turning off friendly errors in MOSS

While in development, the friendly error page that SharePoint displays when our page has an error can make debugging master page issues very difficult.
We can make an easy change to the Web config file for the site to turn friendly error messages off, therefore providing us with more useful information if page breaks. Only do the following in a development environment, and we should never want to turn off friendly error messages in a production environment. Also be sure to make a back up of the file prior to editing.
1. On the Web server, navigate to the site directory:Local Drive:\Inetpub\wwwroot\wss\VirtualDirectories\[directory for site]
2. Open Web.config in Notepad.
3. Search for "CallStack". Change the CallStack status to "true".
4. Search for "CustomErrors". Change the mode to "off".
5. Save and close the file.
Now when the site encounters an error, you will receive a .NET screen outlining the issue instead of the friendly SharePoint error screen. This is particularly useful with dealing with missing Content Placeholders and editing Master Pages. To turn friendly error messages back on, just walk through these steps setting the CallStack to false and CustomErrors mode to On.