Upgrading server OS versions

One of my clients bought a server that was supposed to be the last box they would ever need. Of course, in IT, this is never the case and this one reached its limit when they needed another VM and the existing OS did not support any additional VMs.  So we had to upgrade.  Supposed to be easy right? In theory it is (the difference between theory and practice: In theory there is no difference between theory and practice. In practice, there is) but I was not so fortunate that day.  Luckly one of my colleagues Jamie Belair was there with some wicked Google-fu and managed to find the answer for me.  So here is what happened and what we did.  We were trying to upgrade from Server 2008r2 Standard to Server 2008r2 Datacenter.

I used the commands from my previous post to check the verisons and it was supposed to just work:
http://social.technet.microsoft.com/Forums/windowsserver/en-US/508bc1c1-bd02-4d30-bb55-ffa6e6b6d37a/dism-error-attempting-to-run-online-upgrade-from-windows-server-2008-r2-enterprise-to-datacenter?forum=winserversetup

What we ended up needing to do was install a specific KMS key:
http://technet.microsoft.com/en-us/library/ff793421.aspx

and then switch the key to a MAK key (which we already had purchased)

So in summary we were not able to upgrade to the MAK key without first going to a KMS key…

Get ‘er done!