ORA-01031: insufficient privileges On Windows

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 Continue reading