ORA-12560: TNS:protocol adapter error

Cause :- In my case I have two database in my PC. One is ORCL and another is DBRMAN my default ORACLE_SID is ORCL when I am trying to connect DBRMAN database I get this error.

Solution :- For raising this error you can check after set your SID in which database you want to connect.

SQL> conn /as sysdba
ERROR:
ORA-12560: TNS:protocol adapter error


SQL> exit

C:\Users\rajib.pradhan>set ORACLE_SID=DBRMAN

C:\Users\rajib.pradhan>sqlplus /nolog

SQL*Plus: Release 11.2.0.1.0 Production on Tue Jul 8 11:47:44 2014

Copyright (c) 1982, 2010, Oracle.  All rights reserved.

SQL> conn /as sysdba
Connected.
SQL>