If the Directory Service event log reports Event ID 2095. Here is how to fix the issue:

1. Shut down the domain controller virtual machine that recorded the error, and ensure that it does not restart.

2. Determine whether a snapshot of the domain controller was recently used as a restore mechanism. If so, this is most probably the source of the error.

3. Attempt to determine whether any changes originated from this domain controller and propagated to other domain controllers. If the event was a result of a snapshot or copy of a virtual machine being started, try to determine the time the USN rollback occurred. You can then check the replication partners of that domain controller to determine whether replication occurred since then.

   You can use the Repadmin tool to make this determination. For information about how to use Repadmin, see Monitoring and Troubleshooting Active Directory Replication Using Repadmin (http://go.microsoft.com/fwlink/?LinkId=122830). If you are not able to determine this yourself, contact Microsoft Customer Service and Support (http://go.microsoft.com/fwlink/?LinkID=102491) for assistance.

4. Forcefully demote the domain controller. This involves cleaning up the domain controller’s metadata and seizing the operations master (also known as flexible single master operations or FSMO) roles. For more information, see the “Recovering from USN rollback” section of article 875495 in the Microsoft Knowledge Base (http://go.microsoft.com/fwlink/?LinkID=137182).

5. Delete all former VHD files for the domain controller.

When a running virtual machine is moved to a server running different processor, the virtualization platform needs to provide necessary support to ensure applications running inside virtual machines continue to run on the destination processor. 

The Processor Compatibility new feature of Windows 2008 R2, enables Live Migration to occur between processors at different versions/generations/steppings.

A particular Intel or AMD class of processors exists in a family. That family has multiple generations, or steppings, that define one set of processors from another. While these differences are relatively unnoticeable for most of us during our usual use of the OS, they can be enough to prevent a Live Migration from successfully occurring. The "differences" actually arrive as different processor capabilities that are baked into the chip itself.

This new feature enables the masking of these features so that a running virtual machine can successfully Live Migrate from one host to another. The result is that you must no longer be exactly equal in processor capabilities between multiple hosts. The best part is that the majority of this functionality is kept underneath the covers.

You only need to check if the box "Migrate to a physical computer with a different processor version" is marked for each VM. That’s it. The Live Migration process will eliminates concerns and conflicts and process the migration sucessfully

Scenarios

1. You have a virtual machine running on a host A and would like to be able to move it to another host B   

2. You buy another server and add to the cluster.  The newly added server is most likely has newly added processor features than other hosts in the cluster.  You would like to be able to move running virtual machines freely from any node of the cluster. 

3. You have a virtual machine running on host A, You save the VM with active memory state and would like to restore the same at a later date on any Hyper-V enabled host which may not be the same host.

How it works:

With processor compatibility mode enabled, Hyper-V only exposes the guest VM to processor features that are available across all processors of the same processor architecture, i.e. AMD-to-AMD or Intel-to-Intel. This allows the VM to be migrated to any hardware platform of the same processor architecture. Processor features are “hidden” by the Hypervisor by intercepting a VM’s CPUID instruction and clearing the returned bits corresponding to the hidden features.

When a VM in a processor compatibility mode is started following processor features are hidden from the VM:

Host running AMD based processor
 SSSE3, SSE4.1, SSE4.A, SSE5, POPCNT,
LZCNT, Misaligned SSE, AMD 3DNow!,

Host running Intel based processor
 SSSE3, SSE4.1, SSE4.2, POPCNT, Misaligned
SSE, XSAVE, AVX
 
Also, VM’s cache line flush size is set to 8 bytes on AMD and Intel based hosts when in processor compatibility mode.

Important : Windows Server 2008 R2 Hyper-V will not allow migrating a VM (with or without in processor compatibility mode) from AMD based hosts to Intel based hosts, and vice versa.

VM’s processor compatibility mode is OFF by default.  It can be turned on by one of the two ways:

1. Using Hyper-V Manager: from Hyper-V Manager, select CPU setting wizard of the VM. 
Check a check-box labeled “Migrate to physical computer with a different processor version.  You can only change this setting when VM is not running.

2. Using System Center Virtual Machine Manager 2008 R2

Notes :

1. Moving down to older processer versions consider potential performance reduction due to loss of processor features which might accelerate applications performance. It’s recommended that you properly test these scenarios.   
 
2. An application may use non-recommended methods for processor feature detection, such as instruction probing, i.e. using an exception handler and attempting to execute a feature’s instruction to determine the presence of a feature. Or, basing feature presence on the type of processor, i.e. family, model and stepping. 

3. Applications may fail to launch because of the lack of a specific a processor feature It is recommended that before deploy

To disable the virtual network adapter in a full installation of Windows Server 2008, follow these steps:

1. Open Network and Sharing Center in Control Panel.
2. Click Manage Network Connections.
3. On the View menu, click Details.
4. Double-click the appropriate virtual network adapter in the Name column.

   Note In a default installation, this is the name of the External Virtual Network that was created by Virtual Network Manager in Hyper-V Manager.

5. Click Disable.

netsh interface show interface

netsh interface show interface "InterfaceName" disabled

I really like the Core version and Microsoft is helping us a lot with some usefull comands/scripts.

MS announced that in Windows Server 2008 R2, there’s an easy to use CLI, SCONFIG. SCONFIG dramatically eases server configuration for Windows Server 2008 R2 core deployments. With SCONFIG, you can easily set your system up, get it on the network so you can easily manage the server remotely.

• Rename your computer? Press 2 and you will be prompted to type in the computer name.
• Domain join? Press 1 and you’ll be prompted for name & password.

Simple, EASY and fast.

With SCONFIG you can easily have a Windows Server 2008 R2 Server Core deployment setup in minutes. I should also mention that SCONFIG is also localized in almost 20 languages.

Tasks include:

1. Domain join
2. Rename Computer
3. Configure Remote (Enable management via Server Manager, & PowerShell including properly configuring the firewall.)
4. Configuring Windows Update
5. Enabling Remote Desktop (in case you want to login remotely.)
6. Configuring Networking (static vs. DHCP and for multiple NICs)
7. and more….

All you have to do is type sconfig at the command line.

Dual Core or multiprocessor AMD Opteron processors may encounter Time Stamp Counter (TSC) drift in certain conditions when time precision is important
 
Whether the system is affected by this issue depends on the specific ProLiant server generation, the number and type of AMD Opteron processors installed, the operating system, and whether AMD’s PowerNow! feature is being utilized.
 
This condition affects operations such as network communications and performance monitoring tasks that are sensitive to system time. For example, Microsoft Active Directory domain controllers can report an Unexpected Network Error (Event ID 1054).
Event Description: Windows cannot obtain the domain controller name for your computer network. (An unexpected network error occurred ) . Group Policy processing aborted.

In addition, a negative PING time may be returned after issuing the PING command. The negative PING time occurs because of a Time Stamp Counter drift occurring on AMD Opteron platforms which include more than one processor core.

You may also see that the performance monitor shows you wrong values.

Cause
Many operating systems use the TSC as a timekeeping source. Each processor core (whether it is a single-core processor or dual-core processor) includes a TSC. When the TSC for different processor cores are not synchronized, the above symptoms and behaviors can occur if the operating system is using the TSC as a timekeeping source

Resolution
Edit the BOOT.ini file and add the parameter "/usepmtimer", then reboot the server. Adding the "/usepmtimer" parameter to the BOOT.INI file configures the Windows operating system to use the PM_TIMER, rather than the Time Stamp Counter.
 
Note: When installing the latest AMD PowerNow! Technology driver from AMD, the BOOT.INI file will automatically be updated with the “/usepmtimer” parameter. While the driver itself does not resolve this issue, the installation process will make the necessary changes to the BOOT.INI file to prevent the issue from occurring.

Unless you are running SP2 for W2K3 (where we use the PM timer for MP APIC ACPI HALs by default now), you must force the use of the PM timer on AMD machines via the /USEPMTIMER switch. The decision to use the PM timer versus the TSC is actually a check done on boot to query the BIOS, and determine whether or not it will properly support the PM timer functions – this check is not 100% accurate on AMD chipsets, and that is why forcing /USEPMTIMER is required. This section of code was rewritten for W2K3 SP2, and you should see the proper performance monitor data on AMD chipsets with SP2 installed without the use of the /USEPMTIMER switch.

The document from AMD in the below link also explains the above problem

http://developer.amd.com/Assets/TSC_Dual-Core_Utility.pdf 

http://developer.amd.com/Pages/1214200692.aspx