Basic trigger help

Can any body help me with the following trigger? I is invalid as there is an error in the sql, but when I run this separately it works.

after insert on db.delays
referencing
new as new
old as old
FOR EACH ROW
begin

    if (select c.cgrno from customer c, ad a, delays d

      where a.adno=:NEW.ADNO
      and a.cus2no=c.cusno
      and d.adno=a.adno
      and d.vno=a.vno); <> 100 then
      begin
        delete from delays where adno=:old.adno;
      end;