By default IIS does not display detailed errors to anything but a browser on the local server. This can be a pain if you are using a VM or server with IDE and Browser are on a different machine. This should obviously only be done on a development machine. This being said, open IIS Manager and navigate to Error Pages.
Then Click ‘Edit Feature Settings. Then select ‘Detailed Errors’ to display them to the client. Click OK and restart your web server service to make sure, and develop quicker. For more information look on the official IIS Blog.
UPDATE: When using Windows 7 and IIS 7 with PHP Manager, make sure you open PHP Manager and select ‘Configure error reporting’ and set it to “Development machine”. This will allow output of PHP errors to the browser.