Yet another one of those times where Windows 2008 Server sneaks up on you and bites you in the a$$. So I was installing Exchange 2010 onto our Virtual Lab early one Sunday morning (yes, no life, etc…) and everything was going swimmingly. I’d installed the required hotfixes and all of the Prerequisite Roles (using this great PowerShell script from http://www.telnetport25.com/2011/04/prerequisites-for-installing-exchange-2010-sp1-on-windows-2008-r2/#comment-186) – and was running through the Readiness Checks that form part of the Exchange Server setup process when I hit this problem:
Exchange Setup encountered a problem while validating the state of Active Directory: Could not find any Domain Controller in domain <mydomain.local>
Our lab setup is the most basic one possible, and this was the first product being installed that extends the AD Schema, so when I started seeing that message I was floored. I checked DNS, checked the GC and other AD Roles (hey, with only one AD Server where else could they be?), etc – nothing. Then doubts start to set in… so onto Google I go – went through a couple of websites and then got to the Technet Newsgroups: http://social.technet.microsoft.com/Forums/en-US/exchangesvrdeploy/thread/7aadc4c8-1d0c-4c9a-a46c-884ab66dc922/; The comment that caught my eye was this one:
This may not work for everyone but I am installing on windows 2008 and I ran into this issue. I completely closed out the install and went to the cd and right clicked the setup file and ran as administrator. Seemed to work post this trial.
Sure enough, that was it. Now is it just me, or could the error message be a little better worded? 
Brad
SharePoint Blog 
Thanks Brad. This helped. In the link you provided, there was a mention to delete stale credentials in a key manager:
1. Click Start, click Run, type “control keymgr.dll” , and the click OK.
2. Delete any entry that matches the names of the Exchange servers or domain controllers in your organization
Just an FYI: After the key delete, you cannot “retry” the setup if you already have it going. You must end your current failed install attempt and then restart the install procedure.
I did not test if running “setup.exe” without the “run as admin” works after that.
Thank you for this tidbit. Was beating my head on the wall until I found your post!
Echo all comments. I too was going down the road of “what is wrong with my DNS”?? Thanks!
Thank you!
THANK YOU!
Thanks mate 🙂
In my case, I had few conflicting records present under the “hosts” file. Removed the records and then the setup resumed without any issue.