If you get a PXE E-32 error on your client when using WDS on a 2008R2 server then it is due to DNS stealing a port which WDS needs, this will probably happen following an update.
It can be fixed however with a little tweak in Regedit,
Navigate to HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\WDSServer\Parameters
Change the value of UdpPortPolicy to 0, close Regedit
Restart WDS on the server.
This should allow you to PXE boot properly again.
Thanks to sted over at the edugeek forums for this fix.