I installed Oracle 11G on my Windows 2008 R2 Server. I also installed Oracle Client Libraries using separate installation media. After the client installation, when I try to log into the database using:

C:\>sqlplus / as sysdba

I get a following error:

ORA-01031: insufficient privileges

This worked before the client installation. My account is on the ORA_DBA group. My account is also in the Administrator group. I don't have ORACLE_SID set in my environment variables list. Does it have to be? This worked before the client installation, and I did not have that variable at that time either.

UAC is on at the lowest level, and I always run cmd as admin.

I have an sqlnet.ora file like this in the folder:

C:\app\myaccount\product\11.2.0\dbhome_1\NETWORK\ADMIN

sqlnet.ora

# sqlnet.ora Network Configuration File: C:\app\myaccount\product\11.2.0\dbhome_1\network\admin\sqlnet.ora
# Generated by Oracle configuration tools.

# This file is actually generated by netca. But if customers choose to 
# install "Software Only", this file wont exist and without the native 
# authentication, they will not be able to connect to the database on NT.

SQLNET.AUTHENTICATION_SERVICES= (NTS)

NAMES.DIRECTORY_PATH= (TNSNAMES, EZCONNECT)

tnsnames.ora

# tnsnames.ora Network Configuration File: C:\app\myaccount\product\11.2.0\dbhome_1\network\admin\tnsnames.ora
# Generated by Oracle configuration tools.

LISTENER_ORCL =
  (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))


ORACLR_CONNECTION_DATA =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1521))
    )
    (CONNECT_DATA =
      (SID = CLRExtProc)
      (PRESENTATION = RO)
    )
  )

ORCL =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = orcl.mydb.com)
    )
  )

listener.ora

# listener.ora Network Configuration File: C:\app\myaccount\product\11.2.0\dbhome_1\network\admin\listener.ora
# Generated by Oracle configuration tools.

SID_LIST_LISTENER =
  (SID_LIST =
    (SID_DESC =
      (SID_NAME = CLRExtProc)
      (ORACLE_HOME = C:\app\myaccount\product\11.2.0\dbhome_1)
      (PROGRAM = extproc)
      (ENVS = "EXTPROC_DLLS=ONLY:C:\app\myaccount\product\11.2.0\dbhome_1\bin\oraclr11.dll")
    )
  )

LISTENER =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1521))
      (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
    )
  )

ADR_BASE_LISTENER = C:\app\myaccount

From the windows registry (using regedit), from the path Computer > HKEY_LOCAL_MACHINE > SOFTWARE > Wow6432Node > ORACLE I can find two keys:

KEY_OraClient11g_home1
KEY_OraDb11g_home1

And under those keys I can find ORACLE_HOME variables. So it seem that the client installation generated also ORACLE_HOME so that I have now two ORACLE_HOMEs. I don't know if this has something to do with this problem?

How to resolve this error on my Windows machine?