If on a reboot (**3
Check for Spanning Tree running on the data switches. STP will prevent IP600s from getting DHCP info in a timely fashion, making communication with the TFTP server impossible. It will also reportedly interfere with TFTP in general. If possible on the network, disable STP.
If you are communicating with the TFTP server, but are seeing ACK ignored errors, try a different TFTP server. Solarwinds.net provides a
free version that I've used with good success.