HELP: ORA-12560: TNS:protocol adapter error when I try to connect locally

[Turin]

Hi, I cannot connect locally to my database (without specify the service name) under windows 2000, but when I try to use the service in the "Host string" parameter from the dialog of sqlplus I can connect fine.
I'm receiving this messsage:
ORA-12560: TNSrotocol adapter
Someone know what is happening?, the listener is configured, and my services work fine, but when I try to connect without the service name I cannot connect locally!

I really need your help.
Thank you in advance.

[stecal]

In an MS-DOS window:
set ORACLE_SID=db_name
echo %ORACLE_SID% to verify

System or User variable: set ORACLE_SID to the dbname to make it persistent.

[Turin]

Thank your your answer.
I set the environment ORACLE_SID as you told me, but the error continues ...

Other suggestion ?

Thanks again

[stecal]

You can connect using the net service name, as in
sqlplus username/password@sid

While logged in on the server, you can't connect with a bequeath session, as in
sqlplus username/password

Reason:
The environment variable for ORACLE_SID is unknown to the server. The server knows about the SID when using a qualified connection string (username/password@sid) because the tnsnames.ora file directs the connection to the right place (your server).

This is without ORACLE_SID being set as an environment variable:

SQL*Plus: Release 8.1.6.0.0 - Production on Mon Dec 9 17:55:01 2002

(c) Copyright 1999 Oracle Corporation.  All rights reserved.

Not connected
SQL> conn system/manager
ERROR:
ORA-12560: TNS:protocol adapter error


SQL>

After setting ORACLE_SID again, leaving SQL*Plus, re-starting SQL*Plus:

SQL*Plus: Release 8.1.6.0.0 - Production on Mon Dec 9 17:58:58 2002

(c) Copyright 1999 Oracle Corporation.  All rights reserved.

Not connected
SQL> conn system/manager
Connected.
SQL>