If you work with Microsoft Hyper-v on windows Vista or windows Server 2008 then you no doubt use SYSPREP to prepare virtual machine templates. If you are still building each VM and installing windows from scratch then you are making life hard for yourself, in which case I suggest you read THIS.

When you first install Windows your rearm count is set at 3. You can see the current rearm count by running slgmgr.vbs /dlv and looking at the following:

Remaining Windows rearm count: 3

Note: If you install a service pack the count will increase by 1

When you exceed the rearm count you should get error similar to this KB

929828    An error message occurs when you run "Sysprep /generalize" in Windows Vista: "A fatal error occurred while trying to Sysprep the machine"

When you run the sysprep /generalize command, the activation clock will automatically reset, this ensures that when you first boot up you get the 30 day grace period before license activation. This can only be done 3 times, after this you will no longer be able to SYSPREP that windows installation which. This is incredibly annoying as obviously you need to update your templates occasionally. 
However there is a good reason, as if you could indefinitely reset the windows activation then you would never have to activate windows, thus a free license forever. 
NOTE: This limitation does not exist on windows 2003 and XP.

Thankfully you can bypass resetting the activation clock by using the SkipRearm setting in the Microsoft-Windows-Security-Licensing-SLC component. This enables you to run Sysprep multiple times without resetting the activation clock. 
But you MUST remove this setting or set to 0 on the final running of sysprep otherwise the grace period is not reset(additionally the CMID is not reset which can cause problem with KMS activation).

Useful Articles.

• What is sysprep
• How sysprep works
• Sysprep Command Line Syntax
• Unattended Windows Setup Reference

Read more...

I have had this problem a few times where a server with 2 network cards, 1 for local network and one for internet access, will use the local NIC for DNS lookup by default. If your local NIC uses a DNS server which does not perform recursive lookup, then you will have issues making outgoing connections. this may affect all outgoing connections, such as web browsing, or may affect only certain types of connections such as SMTP or applications (such as ColdFusion) trying to make connections to external sites.

In my case I have had this issue with SMTP, more specifically the Microsoft SMTP service that comes with IIS, it simply would not send mail, and I have had this on a few servers.
If you open command prompt and try to do an nslookup of type=mx then it should tell you which name server it is trying to perform the lookup against, and thus why it is failing.

The solution is actually pretty simple, you just need to change the order in which your network cards are used by the system for dns lookups, so that the external nic with the external dns servers is used first.

To do this, simply open your network connection settings "Control Panel\Network and Internet\Network Connections", and press the ALT button to bring up the file menu (this is the bit you probably didn't know about either), then choose advanced –> advanced settings.
Now in the connections list, just move the external nic to the top.

Restart any services which are having issues and bobs your uncle things should be working again.

Here is a video to show you how to change the settings if you are still confused.
http://screencast.com/t/KBJIwrTzX