Trigger needs dbms_alert declared
I think you may be missing synonym for dbms_alert for adminuser schema. A object grant and synonym both are normally required (unless you own the object).

Try following as sys account, perhaps it will fix the problem.

create or replace synonym adminuser.dbms_alert for sys.dbms_alert;

If you don't want to create a synonym, you should use sys.dbms_alert, if your create a synonym as shown above, using just dbms_alert is sufficient in your code.