AEL logic (following this http://www.voip-info.org/wiki/view/Asterisk+AEL):

context default {
        ipkall_a => {
                begin:
                        goto ipkall;
        };

        t => {
                Answer();
                Wait(1);
                Playback(invalid);
                Hangup();
        };
};

context ipkall {
        s => {
                Answer();
                Wait(1);
                Answer();
                Playback(why-no-answer-mystery);
                Hangup();
        };
};


CLI Error:

Oct 26 07:02:06 NOTICE[3436]: pbx.c:1758 pbx_extension_helper: No such label '(ipkall_a)' in extension 'ipkall_a' in context 'default'
Oct 26 07:02:06 WARNING[3436]: pbx.c:6422 ast_parseable_goto: Priority '(ipkall_a)' must be a number > 0, or valid label