Custom error messages
Use general error message
Here you decide if you would like to use a general error message. If you check this box you will be able to specify a page that handles all the errors that may occur.Specific error messages
In this box you are able to specify a page to handle a specific error message. Just click the "plus"-sign and select an error message and the page of your choice.
In the droplist Status you select the specific error message:
then you select a layout or a content area on the current web page:

Add status
Permission rights! This portlet is add-on functionality.