INDEXING PROBLEMS - HELP!!

I'm running an older version of Informix on an Interactive 5.2.4 Unix. I've been running this application for about 4 years now and lately I'm getting some strange problems. I have a table with a bunch of indexes on it. This table has about 13000 records in it. A routine runs, which selects out all the detail data for an associated header from another table. During the select the app bails out and the error log reads "could not do an indexed read to get the next row". So, I repair the indices and try again. It breaks again! So, I drop the indices and recreate them and try again. It breaks again. So I drop the indices and run with none on on the table and presto it works (but VERRY SLOWWWLY). So I selectively add indices and try after each new index. And it breaks again. I don't get core dumps, just the error above and the resulting corrupted indices. My local informix guy said maybe I have a bad disk or filesystem, so I tried fsck'ing and fsck reports no errors. He said that I should move it to a new disk...I don't have that luxury right now..nor can I upgrade and port right now. What can I try next? Much appreciated....Todd (613) 782-2906 ett@carleton.ca