Note: Please see this blog post for the most updated recommendations on this subject.
EDIT: On 3/12/2008, we have posted a new blog post that talks about the hotfix that we have released for this...
Updated Jul 01, 2019
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Windows 2003 Scalable Networking pack and its possible effects on Exchange
Karsten - we seem to have exactly the same issue here at the moment and we are still working on the problem. Have you managed to resolve your issues yet?