I was setting up NLB on Windows Server 2008 today and encountered this error: “Attempt to install Network Load Balancing failed with error code 0x80070643. Fatal Error during installation”  Upon Googling the error (no, I’m haven’t been converted to Bing quite yet), I didn’t come up with any direct hits, although I did find this blog post on installing MSMQ with the same error code.

The long and short of it is that to install some features on Windows Server, it looks like you need to disable the User Access Control (UAC) first.  The steps to disable it are (as given in the aforementioned link):

1.       Go to Control panel and click User Accounts

2.       Select User Accounts and click Turn User Account Control on/ Off

3.       Un-check the check box beside User Account Control

4.       Close the User Account Window, reboot the computer  and try to install your feature again

These steps worked beautifully for me and allowed me to proceed with installing and configuring NLB for my servers.  As was mentioned in the blog as well, once you have installed your features, it is safe to re-enable UAC on your servers if you would like.

The moral of the story, if something isn’t working quite right in Windows Server 2008, try disabling UAC before you try anything else.