ORA-01274: cannot add datafile – file could not be created

Sometimes you might see this error in a Standby DB and MRP fails:

Fri Feb 05 20:30:04 2016
Media Recovery Log +FRA/dbname/archivelog/2016_02_05/thread_1_seq_60424.32931.903038469
Media Recovery Log +FRA/dbname/archivelog/2016_02_05/thread_2_seq_57484.19935.903038469
Media Recovery Log +FRA/dbname/archivelog/2016_02_05/thread_3_seq_57737.6129.903038467
File #106 added to control file as 'UNNAMED00106' because
the parameter STANDBY_FILE_MANAGEMENT is set to MANUAL
The file should be manually created to continue.
Errors with log +FRA/dbname/archivelog/2016_02_05/thread_3_seq_57737.6129.903038467
MRP0: Background Media Recovery terminated with error 1274
Errors in file /u03/app/oracle/diag/rdbms/dbname/dbname1/trace/dbname1_pr00_14002.trc:
ORA-01274: cannot add datafile '+DATA/dbname/datafile/tbsinstalaciones_dat.569.903038575' - file could not be created
Recovery interrupted!
Fri Feb 05 20:30:17 2016
Recovered data files to a consistent state at change 203534746089
Fri Feb 05 20:30:17 2016
MRP0: Background Media Recovery process shutdown (dbname1)

Now, how to fix and restart MRP?

1:- Check where was left this file#: 

    SQL>  select name, bytes from v$datafile  where file#=106;
    NAME                                                              BYTES
    ------------------------------------------------------------ ----------
    /u03/app/oracle/product/11.2.0/db11203_co/dbs/UNNAMED00106            0

2:- Make sure standby_file_management is set to MANUAL, if not:

    SQL> ALTER SYSTEM SET standby_file_management='MANUAL' SCOPE=BOTH SID='*';

3:- Create datafile in DG (in this case +DATA)

   SQL> alter database create datafile '/u03/app/oracle/product/11.2.0/db11203_co/dbs/UNNAMED00106' as '+DATA';

4:- Set standby_file_management to AUTO to avoid further errors.

5:- Start MRP