Failed to include page &2 in page &1. Error returned: &3
&1 - The parent page (the one that should have contained the include page).
&2 - The name of the child page that should have been included.
&3 - The error returned from the call to the program, that should have handled the include.
This message will be thrown when the call to the program handling the include of pages has ended in error.
Check the previous message in the log, it should contain information from the system error.
Check the OS400 joblog for the application service jobs.