ORA-12154 TNS: could not resolve the connect identifier specified with SQLPLUS

I am using Toad to connect my database and its working fine for me . But when i try to connect with the same credential , i am getting the error message as shown below: ORA-12154 TNS: could not resolve the connect identifier specified Steps: 1. Opened command promt 2. Reach to the path of SQLPLUS (*C:\programs\Oracle\Ora11g\BIN*) 3. C:\programs\Oracle\Ora11g\BIN\sqlplus username@schema_name 4. Enter Password : ERROR: ORA-12154 TNS: could not resolve the connect identifier specified 5. But when i open this with the owner of the schema ,it works for me 6. C:\programs\Oracle\Ora11g\BIN\sqlplus schema_name@schema_name 7. Enter Password: 8. Connected to :...................... So,my question is why my username is not able to connect that particular schema ,while the owner of that schema can connect . Note:I can connect to that schema with my username with Toad ,but not with sqlplus My TNSNAME.ORA is under TNS_ADMIN folder Please help me out of this .