One of our Prod systems is running on Windows server. While I am trying to connect database as sysdba user it throws A-01031: insufficient privileges

C:\Windows\>sqlplus “/ as sysdba”

SQL*Plus: Release 11.2.0.1.0 Production on Mon Apr 27 13:15:06 2018

ERROR:
ORA-01031: insufficient privileges

So here is the steps to can solve issue

1.Check sqlnet.ora file

        SQLNET.AUTHENTICATION_SERVICES should be set to  NTS

2. Verified user to be part of ORA_DBA group, which is missing below

• Check username first

C:\Windows\> echo %username%
helios

•   Check DBA group

c:\Oracle>NET LOCALGROUP ORA_DBA
Alias name ORA_DBA
Comment Oracle DBA Group

Members
——————————————————–
USER1
USER2
The command completed successfully.

3. Follow one of the methods from below to can add your user to ORA_DBA OS group

Option 1:
Using MMMC ( microsoft management console) Add the user ‘helios’ to be part of ORA_DBA OS group

Start => All Programs => orahome1 => Configuration and Migration Tools => Administration Assistant for Windows

Option 2:
On command Prompt Type below

“C:\Oracle\product\11.2.0\dbhome_1\MMC Snap-Ins\ORAMMC11.exe” “C:\Oracle\product\11.2.0\dbhome_1\MMC Snap-Ins\Administration Assistant\orammcadm11”

=> expand Oracle Managed Objects => Computers => <UR Hostname> => Right Click on OS Database Administrators – computer => Add/remove
=> Under Domain Drop down Select your hostname => Select your username => click Add => OK
finally Close your MMMc ( microsoft management console) => save it while closing.

Now try again

c:\>sqlplus / as sysdba