IIS 7 custom error pages being ignored

I've watched several YouTube videos on how to configure custom error pages for things like #404, page not found.

It sure looks easy:

• Start IIS7
• Double click on Error Pages
• Find the error code you are interested in customizing, and (for example) browse and select a different page

By default, the file path for my custom error pages is:  %SystemDrive%\inetpub\custerr

Per my subject line, I could never get a custom error page to display.  So then I went to c:\inetput\custerr and removed/deleted the whole directory.  Still had no effect on the error pages displayed.

Is there some sort of webconfig setting or something else that I'm missing that gets IIS to actually use the custom error pages feature?  Thanks, any comments appreciated.