Did you already search the Microsoft Knowledge Base (form Partner Source Search) for client updates?
There are several ones dealing with web service issues. It is all depending on your exact NAV version (is it really 2009 or 2009 SP1 or 2009 R2?).
E.g. KB 2443436 for 2009 SP1 and R2 deals with wrong UTC.
However, it is recommend to download the latest build for your NAV version and test it there.