connect problem

I got connect problem like this

Oracle7.3.4 for winnt (one machine) :
as " connect scott/tiger" is ok ;
as " connect scott/tiger_at_DB_Instance_ID" it gives TNS : could not resolve the service name ;
as"connect scott/tiger_at_DB_Name ", after using SQL NET to add DB_Name into tnsnames.ora, it gives TNS: unable to connect to destination" .

Oracle8 no such problem . Received on Mon Nov 19 2001 - 13:54:17 CST