ESQL/C, Duplication Check & Error -407

We use an ESQL/C program to process data into Informix tables. To weed out duplication I've tried cursors, selecting into host variables, selecting into temp tables, selecting without into clause, and update statement. None of them could get me through these some 14,000 records of data. It does not bomb at the same piece of data and the great majority of errors from numerous runs are -407, with only very few -408. Here is my thought: as tables grow large, each select statement takes more resources to finish because there are more rows to check. And somehow garbage is not collected away. But I close and free cursors when I use them, drop temp tables as appropriate, begin and commit work when using update statement. Have I missed something? And, could someone please explain to me how exactly I should interpret the sqlca.sqlerrd[4], the offset of error into the SQL statement? I'm running INFORMIX-ESQL Version 5.00.UC2 with INFORMIX-SQL Version 4.10.UD2 and INFORMIX-OnLine 5.00.UC2. Thanks in advance for any pointers. With Regards, Pei-yu Huang