D4 C/S and ORA-03113 error

After moving my Oracle server from 8.0.4 to 8.1.5
my applications experience ORA-03113 ends of communication during query
operations.

I develop the applications with Delphi 4.02 C/S and the Oracle Native
SQL Drivers from Borland. The Ora-Client on my development PC (Win NT WS
4.0) is the 8.1.5 client.

The ORA-03113 error appears only with the 8.1.5 server, I've set up an
alternate server machine with the previous 8.0.4 - everything works fine
when connected to it.

Any experience with this situation?? Only an Oracle error or some
problems with the SQL Link drivers too?