Need help badly getting this to compile. Please Help.

I am trying to upgrade this form but this trigger is stopping it from compiling. Can someone please help me fix this.

begin
   if :old_number is null or :new_number is null
      then raise form_trigger_failure;
   else SET_APPLICATION_PROPERTY(CURSOR_STYLE,'BUSY');
     update_coos(:old_number,:new_number);
      SET_APPLICATION_PROPERTY(CURSOR_STYLE,'DEFAULT');
      end if;
   exception
      when form_trigger_failure then
      Message('YOU MUST HAVE A PROJECT NUMBER TO CHANGE/UPDATE FROM AND TO');
END;

Here is the error message that I am getting when I try to compile the code above.

Compiling WHEN-NEW-BLOCK-INSTANCE trigger on UPDATE_COOS data block...