SCCM 2012 - SCVMM - "PXE-E11: ARP Timeout" error - Building Generation 1 Virtual Machine

Scenario:

In SCVMM, I created a Generation 1 virtual machine with a Legacy Network Adapter. A basic Task Sequence has been created to deploy Windows Server 2012 R2 Standard. DHCP server options are set to 66:(SCCM server name) and 67:boot\x64\wdsnbp.com. The new Gen 1 server is imported into SCCM and placed into the relevant operating system deployment OU. The machine is then powered on in SCVMM.

When the Gen1 VM server starts up, it pulls down a dhcp address before hitting "PXE-E11: ARP timeout" error message followed by "PXE-E38: TFTP cannot open connection":
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Testing:

Just to confirm there was an ARP problem, I built another VM in SCVMM - except this was a Generation 2 VM with a non-Legacy NIC. After being imported into SCCM, the Gen 2 VM server was powered on. It then managed to download the NBP file without issue but then failed the secure boot verification process, with the "Boot Failed. EFI Network. Failed Secure Boot Verification. No Operating System was Loaded. Press a key to retry the boot sequence....":

In an attempt to resolve the issue on the Gen 2 VM I powered off the VM, navigated to the properties of the VM in SCVMM and unchecked the Secure Boot Verification tickbox.......but this simply caused the machine to bomb out even faster ("Boot Failed. EFI Network. No Operating System was loaded...")

Checked the firewall logs - couldn't see any activity from the Gen1 server but it was showing activity from Gen2 talking to the PXE point. The only difference between the two servers was the NICs (Gen1 had Legacy and Gen2 had the standard NIC). Disabled the legacy NIC on the Gen1 server in SCVMM and added a standard NIC. Didn't even get a dhcp address. Re-enabled the Legacy NIC and left the standard NIC enabled, booted the server up and suddenly this happened:

The server pxe booted, popped up in the SMSPXE.log and began to build. I have played around with the NIC combinations at least half a dozen times and always get the same result. 

Fix:

When building a Gen 1 virtual machine it appears that, should you encounter the above error, you may need to include both a Legacy and non-Legacy network adapter when building the VM in SCVMM. Both adapters need to be active and plumbed in to the appropriate network/VLAN before the machine can successfully start the build. Once the machine has built you can remove whichever NIC you no longer require.