Ok. Here what's mentioned in the Web Service Security Guide:
http://www.microsoft.com/downloads/details.aspx?FamilyId=3E02A6C8-128A-47C2-9F39
-4082582F3FE1&displaylang=en

<excerpt>
WSE 3.0 and WSE 2.0

Because of changes in the underlying specifications for WS-Addressing,
WS-Trust,
and WS-SecureConversation, WSE 3.0-enabled applications do not interoperate
with
WSE 2.0-enabled applications. However, WSE 3.0 and WSE 2.0 client
applications can
run side-by-side with the .NET Framework 2.0. You can host WSE 3.0-enabled
Web
services and WSE 2.0-enabled Web services on the same computer, but they
must be
in separate virtual directories for ASP.NET or separate applications for
Windows
Forms applications. It is theoretically possible to develop Web services
using WSE 2.0 in such a way
that they can interoperate with WSE 3.0 (and WCF) by using only a reduced
set of
specifications - specifically, SOAP 1.1, WSDL 1.0, and WS-Security 1.0.
However,
Microsoft does not support interoperability in this situation. The safest
way to plan
for interoperability with WCF is to upgrade the WSE 2.0 code to WSE 3.0.
</excerpt>

NOT good. How am I to address an orchestration scenario where many ISVs are
upgrading thei respective web services sporadically (and certainly not in
unison)?  IMHO, the WSE 3.0 team should take some time to address the
interop problem with two of their own products. It is certainly possible;
that's the "soft" in software.

Kindest Regards,
Michael