By more than 8 Threads only: I/O-Exception: The Network Adapter could not establish the connection

Hi all.
I'm fighting with a strange problem for several days already. Maybe
someone can help...
My problem:
I have a Win2K PC with Oracle 10 and Weblogic 6 SP6 installed on it.
JDK is 1.3.1-b24 (that comes with weblogic 6).
I have an application deployed on Weblogic and a JUnit test suite to
test some workflows of my app. I can run the tests parallel with
several threads to simulate the simultanous usage. Everything works
fine if I'm under 8 Threads. By >8 threads the PROBABILITY of error
growth. It can be, that all e.g. 10 Threads are done successfully. But
SOMETIMES there are 2 or 3 failures! In Weblogic's trace there is an
exception then:
java.sql.SQLException: I/O-Exception: The Network Adapter could not
establish the connection
I've just
I suppose, there is smth. wrong with my Oracle/Weblogic settings, but
have no idea what to check. Has someone got something compareable? I
would appreciate any input very much. Thanks.