11.2.0.2 Startup Upgrade Results in ORA-01092, ORA-39701

Issue:
SQL> startup upgrade
ORACLE instance started.

Total System Global Area  784998400 bytes
Fixed Size                  2230600 bytes
Variable Size             482346680 bytes
Database Buffers          293601280 bytes
Redo Buffers                6819840 bytes
Database mounted.
ORA-01092: ORACLE instance terminated. Disconnection forced
ORA-39701: database must be mounted EXCLUSIVE for UPGRADE or DOWNGRADE
Process ID: 7112
Session ID: 125 Serial number: 5


Action:
Add line cluster_database=False to init<sid>.ora  if SPFILE is being called or
Modify cluster_database=False if pfile is being used.

Example, in my case, where spfile is used.
SPFILE='+DATA/<dbname>/spfile<dbname>.ora'
cluster_database=false

SQL> startup upgrade
ORACLE instance started.

Total System Global Area  784998400 bytes
Fixed Size                  2230600 bytes
Variable Size             482346680 bytes
Database Buffers          293601280 bytes
Redo Buffers                6819840 bytes
Database mounted.
Database opened.
Now, @catupgrd can be run.

Note: Do not forget to change cluster_database=True after the upgrade