Application Express :: Showing A Message From A Button?

I have a button with an dynamic action , with sql:

declare
errors varchar2(100);
begin
apex_application.g_print_success_message := 'test message';
errors:=package.function_some_process_returning_varchar100_with_errors_or_sucess;
HTP.p ('<script language="JavaScript"> alert('''||errors||'''); </script>');
end;

The first "test message" is not shown.and after the function (it is executed fine) i get the next error:

Error:Parsererror - SysntaxError: Unexpected token <

i i only leve the first line (g_print_sucess) nothing occurs clicking the button.

I only want to show on a popup the result from the function, but g_print_sucess seems not to work for some reason.