Using CIsam files in Informix SE... some problems...

I have a problem. I have an Informix database set up and need to read data from an application that used CIsam files. I have access to the CIsam files and the file definitions but no control over them apart from that. They are generated on the same machine as my Informix db. What I've done, is this. Set up the db with tables conforming to the CIsam file definitions. Then I copied the CIsam files over the top of the appropriate .dat and .idx files. All looked fine and I could do simple queries. However, some of the complex queries caused a network receive failure. SO... I set up 2 databases. One clean and empty and the other being the one to copy the CIsam filres into. Then I'd unload from the CIsam-copied db and load the unloaded data into the "clean" db. Again it seemed fine. However I now have a problem. On one table in the database with the copied CIsam files, unload doesn t work. Although all the data is in the table when I unload only about 2/3 gets copied to the ascii file. I think it's because of some bad data or else my schema definition for that table doesnt correspond exactly to the ISAM file. I've checked them both and it seems OK except in the CISAM file there's a union of char(12). I've defined this in the schema for the corresponding file as 12 fields of char 12. Other CISAM data types are long, double, integer and float. I really need the data in the database. I can't modify the CIsam files. What can I do????? Thanks, Kate