Hi all, hope someone can help me.

I have a VMWare host with three virtual servers. One we call the DC, running Server 2012 and AD, GP Management, DNS and DHCP, the other two are Server 2008 R2 and run SIMS and Exchange. The Exchange server was originally a single physical server running all three of the roles now being performed by individual servers so it was a DC; we P-to-V'd the original and we created a new DC and made it the primary DC leaving the Exchange server as a secondary DC, with AD, DNS but not DHCP.
It's this new DC that keeps apparently falling off the network. Every other morning or so I need to reboot the machine via VSphere. As soon as it is rebooted users can log in to the network.
I would have thought the secondary DC would jump in if the primary was not available but don't have any idea how that process is instigated or set up. In addition to these issues I don't think things are replicating; there are policy files which are not the same in my sysvol folders.
I can't see anything obvious in the event logs on the primary DC except a multitude of group policy errors that all refer to the same policy file, which I believe is for IE 10+ settings and which is a file that appears on the secondary DC but not the primary DC.

The processing of Group Policy failed. Windows attempted to read the file \\<domain>\SysVol\<domain>\Policies\{0337B1C4-CA85-4BF8-88B2-1A073A0C2059}\gpt.ini from a domain controller and was not successful. Group Policy settings may not be applied until this event is resolved. This issue may be transient and could be caused by one or more of the following:
a) Name Resolution/Network Connectivity to the current domain controller.
b) File Replication Service Latency (a file created on another domain controller has not replicated to the current domain controller).
c) The Distributed File System (DFS) client has been disabled.

The other two VMs seem OK and they all use a single physical NIC so I'm not tempted to think it's anything to do with the hardware or host.

This may not be much to go on in terms of someone being able to help me out but any suggestions would be very welcome.