WDS 2012 R2 Server

Solution 1:

In networking when things sometimes work and sometimes do not there's surely a timing issue involved...

I would alternative try

1. Eliminate the PXE Response Delay 5 second

2. Set the TFTP Max Block size to 1456

3. If possible disable Multicast capabilities.

Edit 1:

Also if the failing TFTP transfers immediately abort after the TFTP request it might be a port issue. TFTP transfers require a random UDP port selected in a per-transfer basis (in your case from 64001 to 65000). If the randomly selected port is either blocked by a firewall or used by some other application you transfer will abort.

Solution 2:

I got the error message before. It is a firewall issue. On my test environment using Hyper-v I turned off firewall on Domain networks and it worked.