How can I create a Pooled VDI infraestructure using Win server 2012 as VM image?

Hello

I have followed the "usual" way to build a pooled VDI desktop using Win7 or Win8 with success, but it fails when I use an image of Win Server 2012 as VM instead. 

Am I overlooking something?  Should I need to prepare the image in a different way? (Sysprep differently?)

Thanks