While an earlier Nvidia communication implied it will fix this issue in A02 silicon it hasn't managed to do that yet. The problem will be fixed in A03 silicon.
All of the early Nforce 4 motherboards that you will get from now till A03 silicon will be limited to 4X HT. For the record, Nforce 3 250 has 5X HT that is working without any problems. You sort of need that to unleash the full power of Athlon 64 939 CPUs that can use 5X and 1000 MHz HT.
Nvidia discovered that its Hypertransport RX input receiver pads have sensitivity that's higher than acceptable to inbound inter symbol interference. Nvidia continued: "This can cause degradation of signal integrity which prevents achieving 5X speed."
A workaround is very simple. You just limit your board to 4X or should we say 800 MHz and not the 1000 MHz that 5X should give.
Nvidia also has some PCIe problems that will be fixed in A03 silicon, whenever it arrives. µ