In central admin in thw Web Application screen. When I click on extend on my web application I get an error message.
The web application could not be extended because an unused zone could not be found. Unextend the web application from the zone that you intend to use for the new IIS web site before performing this operation.
How can I go about debugging this error?
This is indicating that all of the alternate access mapping zones have been utilized for this web application. Check your alternate access mappings and remove some that are not needed so that you can extend your web application into a zone. You have to have at least one zone free (intranet, extranet, custom, internet) to extend a web application. The default is what is created when the web application is first created.
You can take "correlation Id" and try to find stack trace in sharepoint log (C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\LOGS).
