Turn Verbose Error Messaging In SharePoint On

An annoying and easily fixed issue you will see on development machines is the really unhelpful message "An unexpected error has occurred." Open your web.config file, found by default here C:\inetpub\wwwroot\wss\VirtualDirectories\80, and make two changes. The brave will not backup the web.config file first !    

<customErrors mode="Off" />

<SafeMode MaxControls="200" CallStack="true" DirectFileDependencies="10" TotalFileDependencies="50" AllowPageLevelTrace="false">