Error on Illustra

I'm running into this error running Illustra 3.2 on NT: * select count(*) from tablename where column_1 = 'value_1'; W01SS1:warning: W01SS1:warning: XS1003:Lock manager: TABLE_ID <1> The table has about 1.5 mil records and the error occurs only when criterion will meet a subset grater then approx. 15,000. Also, this will happen only when index is built on the column_1. We used: create index index_column_1 on tablename using btree(column_1); If index is not built, there will be no error but the performance will decrease 100 fold rendering the system unusable. Any help highly appreciated. Thanks, Voja. * select count(*) from yu_adresar_i where prezime = 'JOVANOVICH'; --------------- |count | --------------- |8072 | --------------- one row selected