ORA-38856: cannot mark instance UNNAMED_INSTANCE_2 (redo thread 2) as enabled

Issue :

alter database open resetlogs;
*
ERROR at line 1:
ORA-38856: cannot mark instance UNNAMED_INSTANCE_2 (redo thread 2) as enabled

Cause:   When try to open database with resetlogs option after restoring rac db on non rac db.  

Workaround:
 1._no_recovery_through_resetlogs=TRUE set in pfile
 2.startup mount
 3.alter database open resetlogs;