ORA-15150: instance lock mode 'EXCLUSIVE' conflicts with other ASM instance(s)

This is a new standalone server using ASM and crs.The database is not clustered so cluster_database and RAC options are turned off for DB and ASM as expected.

SQL> startup nomount

ORA-15150: instance lock mode 'EXCLUSIVE' conflicts with other ASM instance(s)

We were able to start the database using srvctl start database -d command but not using sqlplus.

The cause of the problem was some parameter in the spfile used by the DB instance when were using sqlplus (I was suspecting it to be instance_number)

To resolve the issue we did the following.

Since the DB was able to start with using the srvctl command,we started it and created pfile from the spfile.Then we used this pfile to start  the instance using sqlplus.

This issue could be caused by some other  reasons in the cluster environment which could be due to following.

• Cluster_database parameter is set to false in ASM/database
• RAC option is not turned on.To turn on RAC option use the following oracle note

How to Check Whether Oracle Binary/Instance is RAC Enabled and Relink Oracle Binary in RAC (Doc ID 284785.1)