ORA-00001: unique constraint (owner.IDX) violated => owner.idx is not a constraint.

hi
oracle return the error ORA-00001: unique constraint (owner.IDX_NAME) violated to my application. but owner. IDX_NAME is not a constraint and is not a unique index.
I verify in

dba_indexes, the index IDX_NAME is not unique,
dba_constraints, the contraints IDX_NAME does not exist

what-is the problem ?

thanks for your help,
Pascal

edit because I forget ORacle 10.2.0.4 on linux x86_64 bits Read 2.6.9-67.ELsmp