TFTP Open Timeout
I’m running a server 2008 R2 box. Having DNS service running on the same machine as WDS causes DNS to steal the ports that TFTP needs.
Run regedit (with Admin access obviously).
Go to HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\WDSServer\Parameters
Right-click UdpPortPolicy, and click Modify. In the Value data box, type 0, and then click OK. Exit Registry Editor and then restart the Windows Deployment Services service.
Worked a treat for me.