Well, I don't know AppConfig, but, from what you've posted, ERROR needs a subref (that's what "\&my_error" is -- a reference to a subroutine called my_error).

What you've used is a subroutine call. You need to change it to ERROR  => \&hanlde_errors, (note: OP's typo untouched) assuming you've got a sub hanlde_errors { ... } somewhere.