How to rollback transaction using COM?

I have n-tier application, which similar to Duwamish v3.5. It's already implemented one month ago, now i found a problem a transaction can not rollback using GETOBJECTCONTEXT.SETABORT.
What must i set to my DAL (Data Access Layer), and BLL (Business Logic Layer)?

Thanks in advance....

Study the usage of Transaction setting from MSDN.
Implementation depends on application.
and use Dim Objcon as objectcontext
set objcon=getobjectcontext(() in all methods and use setabort in a single method from which all
other methods are called if all are true
setabort from orginal place.this is simple