ORA-1502 unusable local index unique key

Oracle 9.2.0.4
32 bit Sun Solaris

The team that loads the data got the following error ORA-01502: index 'CIRXXX.C_XXX_IX01' or partition of such index is in unusable state.
This is a local unique b-tree index on two columns. I'm assuming the got the error during an sqlloader session but I will verify. The load would be conventional. Only some of the index partitions were marked as unusable. Two partitions now have duplicate keys. No DDL was issued on the table. They do a delete followed by a sqlloader session. I've searched metalink and I know there are lots of assm bugs. This tablespace has manual segment space management with system local uniform extents.
I'm wondering if anyone has any ideas on how the dup keys would get in. The constraint is not invalidated or deferred before the load. The user loading the data only has insert/delete privileges on the table.

Thanks
Mike

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