Hi all
I have a table that is partitioned based on month. The partitions are

200412
200501
200502
200503
200504
200505
200506
200507

I also have an index ('WIPMON.KFLOWF_INDEX1') that is based on the table. The index is not partitioned. Yesterday I dropped the partition 200412 from the table.
But when I performed an insert into the table today, I got the following error

ORA-01502: index 'WIPMON.KFLOWF_INDEX1' or partition of such index is in unusable state

What could be the cause of the problem? Must I rebuild the related indexes after I drop any partition?