Index in unusable mode during direct load w/ singlerow

Hi,

We have a range partitioned table, there's sqlldr running in direct mode w/ SINGLEROW option on 1 of the partitions, meanwhile there's a procedure who queries the table using the partition key as the only predicate. Every once in a while, we get an ora-1502 "index '%s.%s' or partition of such index is in unusable state". I thought using SINGLEROW should avoid such error?

The db is 9.2.0.6. happens on both hp and sun platform.

Thanks! -Jessica

--
http://www.freelists.org/webpage/oracle-l