Oracle DB connection problem

Hi everyone

I'm getting the following Oracle db error connection message sporadically trying to connect to the db from the server. It did work some times (1st & 4th) but other times failed (2nd & 3rd) - Any ideas?

Thanks
Chris

$ sqlplus username/password_at_dbname

SQL*Plus: Release 8.1.5.0.0 - Production on Wed Jul 3 11:58:06 2002  (c) Copyright 1999 Oracle Corporation. All rights reserved.

 ERROR:
ORA-12537: TNS:connection closed

Enter user-name:
ERROR:
ORA-01017: invalid username/password; logon denied

Enter user-name: ^C

$ sqlplus username/password_at_dbname

SQL*Plus: Release 8.1.5.0.0 - Production on Wed Jul 3 11:58:32 2002 (c) Copyright 1999 Oracle Corporation. All rights reserved.

Connected to:
Oracle8i Enterprise Edition Release 8.1.5.0.0 - Production With the Partitioning and Java options

PL/SQL Release 8.1.5.0.0 - Production
SQL> exit

$ sqlplus username/password_at_dbname

SQL*Plus: Release 8.1.5.0.0 - Production on Wed Jul 3 12:04:34 2002

(c) Copyright 1999 Oracle Corporation. All rights reserved.

Connected to:
Oracle8i Enterprise Edition Release 8.1.5.0.0 - Production With the Partitioning and Java options

PL/SQL Release 8.1.5.0.0 - Production
SQL> exit

$ sqlplus username/password_at_dbname

SQL*Plus: Release 8.1.5.0.0 - Production on Wed Jul 3 12:04:49 2002

 (c) Copyright 1999 Oracle Corporation. All rights reserved.

ERROR:
ORA-12537: TNS:connection closed
Enter user-name: Received on Fri Jul 05 2002 - 04:23:01 CDT