does only

SEROUT SO,16468,["HELLO",10]

works alone ???

if not try

SEROUT SO,4,["HELLO",10] ;2400 baud inverted

Do you use MicroCode studio to get your data from RS232? If yes, Be sure of the selected BaudRate.

In case of SEROUT SO,4,["HELLO",10] don't work, try
SEROUT SO,0,["HELLO",10] ;2400 true


regards