ORA-12720: operation requires database is in EXCLUSIVE mode

When I try to create a controlfile for a RAC database using the CONTROLFILE Trace. It threw the below error message:

CREATE CONTROLFILE .................................
   .................................................
CHARACTER SET AL32UTF8;

ERROR at line 1:
ORA-01503: CREATE CONTROLFILE failed
ORA-12720: operation requires database is in EXCLUSIVE mode

Solution:

SQL> alter system set cluster_database=FALSE scope=spfile sid='*';
shutdown immdeiate;
startup nomount;

re-run script for controlfile creation

CREATE CONTROLFILE .................................
   .................................................
CHARACTER SET AL32UTF8;

Control file created.

after that change parameter with its old value

SQL> alter system set cluster_database=TRUE scope=spfile sid='*';

and restart database.