So the other day I was working on a VM and I needed to add an additional HD to it.  This is easy enough, after I added this I went into Disk Management in Windows 2008 and formatted it.   Then, for some reason, I selected "Mark Partition as active"; a warning message popped up which I ignored and moved on.  Everything was working great.  I setup the HD for the application I was working on, everything was right with the world... until I rebooted the VM.<!--more-->

Ya... don't change the active partition.  That warning message was trying to tell me that the active partition needs to be assigned to the OS partition.  Opps!  I figured the fix is easy enough.  I booted the machine using a Windows 2008 ISO, went into repair mode, brought up a command prompt and used diskpart to change the active partition using the following commands:
<ul>
	<li>select disk X</li>
	<li>select partition X</li>
	<li>active</li>
</ul>
I rebooted again and still had a failure.  This is why I decided to make a blog post about this error.  I learned that the active partition is not the C: which I would assume it is... its actually that 100MB system drive that Windows 2008 makes.  I had to run through the command line again and this time select the system partition and make that one the active.  Again, this is all pretty simple stuff, but it caught me off guard.  I never knew that the 100MB partition was the active.  Now I know, and so I share it.

-Gunnar