This error indicates that there is something wrong with the histogram statistics either in the data dictionary or just in the dictionary cache. There are several known bugs that can cause this. They are all fixed by release 8.1.7. Until then the "workaround" is to reanalyze the table using the COMPUTE STATISTICS option.

I have found the following error from the alert.log.

Errors in file /u07/oradata/aoufslq/udump/ora_4440_aoufslq.trc:
ORA-00600: internal error code, arguments: [16515], [D], [40], [31027], [5], [0], [], []