Joseph DeVore's Blog: Master page debugging when branding SharePoint sites

I've been doing a lot of SharePoint master page customization lately and OOTB, SharePoint traps any exceptions by default. If you have a syntax error or are missing a required ContentPlaceHolder, you'll receive a friendly error message and have no idea of why your new master page won't work.

If you want to save yourself some time and some hair - just turn off Friendly Errors!

On the web server, navigate to the site directory for your SP site: c:\inetpub\wwwroot\wss\VirtualDirectories\[site]

Open: Web.config in Notepad.

Search for: CallStack and change the CallStack status to: true.

Search for: CustomErrors and change the mode to: off.

Save and close the file.

Now when you receive an error, you'll get the .NET debugging information.