I’ve recently rebuilt my home lab environment to run Windows Server 2012 with Hyper-V 3.0. After installing the ConfigMgr 2012 console on it, I was attempting to create new task sequence media when I received an error that the directory name was invalid. I tried different file locations to save the .iso, such as c:\, d:\ (an external USB device), my desktop, and a UNC path. All failed.
Figuring that this was more a problem with “user account control”, I launched the console with elevated permissions and the error did not occur. But to see if there was some other problem, I then launched the console normally and when creating the boot disc again, Windows Server 2012 then correctly prompted to allow for to allow execution.
It’s an odd problem, but if it occurs for you, first try just restarting the console!