I was trying to Migrate Database to ASM by using the following steps but got error at step3,can anybody help me in this regard?

step1:Set DB_CREATE_FILE_DEST and DB_CREATE_ONLINE_LOG_DEST_n (where n=1-4) to refer to the desired ASM disk groups.
For Example
Alter system set DB_CREATE_FILE_DEST=’+DGROUP1’ scope=spfile;
Alter system set DB_create_Online_log_DEST_1=’+DGROUP1’ scope=spfile;
Alter system set DB_create_Online_log_DEST_2=’+DGROUP1’ scope=spfile;
Alter system set DB_create_Online_log_DEST_3=’+DGROUP1’ scope=spfile;
Alter system set DB_create_Online_log_DEST_4=’+DGROUP1’ scope=spfile;

step2:alter system set control_files='' scope=spfile;

step3: SQL>shutdown immediate
step4: RMAN>startup nomount;

ORA-12528: TNS:listener: all appropriate instances are blocking new connections

step5: RMAN>restore controlfile from 'old_controlfiles_location'
step6: RMAN> ALTER DATABASE MOUNT;
step7: RMAN> BACKUP AS COPY DATABASE FORMAT '+DGROUP1';
step8: RMAN> SWITCH DATABASE TO COPY;
step9: RMAN> ALTER DATABASE OPEN;