SQL Error: ORA-14300: While partitioning and subpartitioning
I had to explicitly define all my range partitions. Interval partitioning did not work well with sub-partitioning template.

Oracle does HARD Limit of 1m partitions to my interval partitions.

I defined partitions as

PARTITION jan06 VALUES LESS THAN (TO_DATE('01-FEB-2006','DD-MON-YYYY')),
...
ALL THE WAY FOR NEXT 20 YEARS..
...
PARTITION jan26 VALUES LESS THAN (TO_DATE('01-FEB-2026','DD-MON-YYYY')),


Refer here and there