Problem Connecting To SQLPlus

Following a clean installation of Oracle 8i, I cannot log into SQL-Plus. I use the stock account that comes with install, that of "system/manager" and it responds with:

oracle_at_tillarium:~$ sqlplus

SQL*Plus: Release 8.1.7.0.0 - Production on Sun Jun 30 12:22:35 2002

(c) Copyright 2000 Oracle Corporation. All rights reserved.

Enter user-name: SYSTEM
Enter password:
ERROR:
ORA-03113: end-of-file on communication channel

Any ideas on how I can solze this problem of having no user accounts?

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Information and comments are appreciated.

Robert