Earlier today I had the opportunity to troubleshoot a ConfigMgr 2012 R2 SP1 CU1 server that could happily PXE boot Generation 1 VMs, but not Generation 2 VMs. The SMSPXE.Log had really no info than it tried to serve the wdsmgfw.efi to the client. but then nothing happened.
The error that was displayed on the client was simply:
No Operating System was Loaded. Press a key to retry the boot sequence…
It turned out that simply deleting the files in the RemoteInstall\SMSBoot\x64 folder, delete the RemoteInstall\SMSBoot\boot.sdi file, and then restart WDS Service to have them recreated automatically solved the problem.
Happy Deployment, Johan