config reserved means that the Mitel DHCP server issues the phone an IP address, however the phone did not respond. if the firmware is older in your 5201's make sure you do the OLD way of setting up the DHCP server using the separate options 128-130, as opposed to the DHCP option 43 / 125 way... I have found more than one case of a 5201 sitting on the shelf with very old firmware in it so it wont recognize the newer DHCP scheme until it boots all the way up and downloads its firmware from the PBX...
-Christopher