One thing you may not know is that when you add a disk to a Windows 2012 virtual machine under vSphere 5, it gets added and tagged as removable. The consequence of this tag is that when you try to access that disk using \\servername\e$, a popup message appear:
"Windows cannot access \\servername\e$
You do not have permission to access \\servername\e$. Contact your network administrator to request access."
If you look on the security log of your Windows server: an audit failure should have appeared