SQL & PL/SQL

Hello, I have recently locked a partition,p_200404, in TABLE_M using:

lock table TABLE_M partition (p_200404) in exclusive mode nowait;

Any DML on this partition gives the error:

ORA-01502: index 'table_M index' or partition of such index is in unusable state

and when i try to rebuild the index using:

alter index 'table_m index' rebuild partition p_200404

it gives me the error:
ORA-00069: cannot acquire lock -- table locks disabled for TABLE_M.

What i want to do is unlock this partition, but, not exactly sure how. I know it says to free the lock you have to perform a COMMIT, ROLLBACK, or SAVEPOINT, but, what is the syntax for this? I've tried
to simply drop the whole table but again I get the ORA-00069 error. Please help.


Thanks,

Tin Hoang