ORA-12571, -01041, -01092 error messages 8iPE 8.1.5

I bought a PE licence Oracle 8i 8.1.5 for WinNT. After I installed the database and created some tables, I experienced some problems: I run some SQL queries with SQL*Plus. After a couple of minutes the database became inaccessible: First I got Error ORA-12571: TNS:packet writer failure. When I tried to run the same SQL again, I received ORA-01041: Interner Fehler: hostdef-Erweiterung existiert nicht (now it's German: internal error: hostdef-extension doesn't exist). After shutting down SQL*Plus and restarting it, I received ORA-01092: ORACLE instance terminated. Disconnection forced. It happens all the time. It'd no problem with the SQL, because the same SQL worked properly before (it was just a select * from <table>;).
Who can help?
Best regards,

Dirk

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Before you buy. Received on Sun Apr 30 2000 - 00:00:00 CDT