invalid row id...

In the process of running a data load, we always encounter an assert failure message that there was an invalid row id, where a record is read. What does this mean? It also specified a 'partnum' and it was pointing to a certain hierarchy table. How can we identify which record had the invalid row id? Was this caused by garbage in the data being loaded? How can we prevent this from occuring again? We are using Informix On-line Server version 7.20 on a HP-UX 10.10. Thanks for any help.