oracle - ORA 12154 - unable to connect from toad/SQLplus -

when try connect database in tnsnames.ora file sqlplus throws

ora-12154: tns not resolve service name 

i've checked stuff:

tns_admin environment variable defined "c:\oraclexe\app\oracle\product\10.2.0\server\network\admin"    "c:\oraclexe\app\oracle\product\10.2.0\server\network\admin\tnsnames.ora" located    following connect descriptor found my_db in tnsnames.ora file    my_db=     (description=       (address=         (protocol=tcp)         (host=local.db)         (port=1521)       )       (connect_data=         (sid=scmprod)       )     )    "c:\oraclexe\app\oracle\product\10.2.0\server\network\admin\sqlnet.ora" located    names.directory_path specifies tnsnames in sqlnet.ora file   

the question is:

what missing?

update

now on sqlplus using the usr/pwd@selftest connection string works

in can't error on server because on old pc still accept connection company works on it.

the tnsname.ora

selftest=   (description=     (address=       (protocol=tcp)       (host=10.100.2.7)       (port=1521)     )     (connect_data=       (server=dedicated)       (service_name=goldtest)     )   ) 

the problem still exist trying connect toad oracle...

ora-12154: tns not resolve service name

my_db=     (description=       (address=         (protocol=tcp)         (host=local.db)         (port=1521)       )       (connect_data=         (sid=scmprod)       )     ) 

the error incorrect service name. see tnsnames.ora doesn't have service_name, rather have mentioned sid. cause of error.

you edit tnsnames.ora as:

scmprod =  (description =     (address_list =      (address = (protocol = tcp)(host = localhost)(port = 1521))    )  (connect_data =    (service_name = scmprod)  ) ) 

assuming, scmprod service_name.