Oracle, multi thread and heavy load leads to access violation in ORA73.dll

We have the following environment:
- Oracle Server 7.3.4.5 on HP-UX 10.20
- Oracle Client 7.3.4.5 on Windows NT 4.0 WS + SP5
- Direct Oracle Access 3.3.1
- Delphi 4 + update 3

The problem is that when the load rises (50 transactions/sec) the
client-side ORA73.dll starts to throw access violations. We have tracked
this one with Oracle support to no avail (upgraded, patched etc.). The
problem does not occur if the load is lighter. The same queries are
repeated
over and over again so the problem shouldn't be on our application.

Problem persists on every machine we have tried and is repeatable. What
makes it {*word*193} is the fact that ORA73.dll does not recover until
application is restarted (and thus dll is initialized). Also we haven't
been able to track down the responsible party, it could Oracle server or
client, DOA or our application.

We have traced SQL*Net and found out that when a select query is
executed atleast four relevant packets are sent/received:
- Query itself (to transport)
- Received column names (from transport)
- Request for the data (to transport)
- Receive the data (from transport)

When the error occurs the last two packets are missing. Don't know if
this means anything because these could just be symptoms not the cause.

Any help or hint will be greatly appreciated!

--
Henri Suuronen