Windows 7 64-bit guest network connectivity issue

[Rich Miller]

Running Windows 7 64-bit host with 8GB RAM and Windows 7 64-bit guest with 2GB RAM on an ASRock P45R2000-Wifi motherboard with an E8500 CPU. It has a P45 North Bridge and an ICH10R South Bridge. The Wifi module is not installed. It has dual NICs which are RealTek RTL8111B/RTL811C, one of which is disabled. The guest NIC is a bridged Intel Pro 1000/MT adapter. In VirtualBox 3.1.0, a 64-bit guest does not acquire a DHCP address, but a 32-bit guest will. Using a static IP address doesn't work either. Changing the guest mode to NAT or Host-only Adapter doesn't help either. The host driver for the NIC is provided by Microsoft, so I also tried installing the latest driver from RealTek, but there was no change. If I roll back to 3.0.12 or 3.0.10, the guest acquires a DHCP address and has a default gateway, but still has no connectivity. Even though it has acquired an IP address, I can't even ping the gateway.

A few days ago, I copied the Virtual Disk Image to a portable drive and took it to my home machine which is similar. It has an MSI MS-7519 P45 Neo-F motherboard with a Q9550S CPU with 8GB of RAM, also running Windows 7 64 bit. It has a P45 North Bridge and an ICH10 South Bridge, and also has (a single) Realtek RTL811C NIC. With the same virtual machine settings as my office computer, that configuration runs fine under 3.0.12.

I reinstalled 3.1.0 and now my office computer is acquiring a DHCP address, but still can't ping the default gateway.

I know it doesn't make any sense. Let me know what other information you need.