I deleted my .NETMF and Netduino SDKs and downloaded and installed the latest 4.2. I took an unused (4.1.0.6) Plus board, erased it using the pad, loaded the boot with SAMBA, loaded the 4.2RC5 firmware and config with MFDeploy without problem. Afterwards, Ping, no response. Started over again with boot, firmware, config, still no response. Unplugged the USB cable, blue screen, reboot, launch MFDeploy Ping OK, restored the MAC. Ping, no reply. Tried deploying my code from VS no go. The board will occasionally respond to MFDeploy and reports correct MAC but I have not been able to deploy from VS at all. Tried various USB ports, reset button pushes, reconnects, nothing.
Have you tried to restart (from the onboard button) the N+ and ping it again? You using static IP? I´ve have noted that mine board seems works OK with DHCP, or the restart. But on other two boards, from friends of mine the network apparently worked fine on preliminary tests.