-565 ERROR + -101 ISAM error with 5SE

-565 : Cannot read sorted rows. -101 ISAM error : file is not open. I got this error in the following context : SCO server with informix SE 5.01.UD3. The file quota per process is 256. Windows NT client via Inet. Within a transaction, we do a SELECT ... ORDER BY col, then some UPDATE/INSERT and SELECT . The error comes later, before the commit, after a fetch on the first query. If we look the opened files on Unix side, just have 64 opened files;On the client side, may be 15 statemenets pending. The problem is solved if we don't use transaction or leave the order by clause from the first select... Is anybody award of that possible limitation of SE. And how to turn around this problem ? Thanks