I had a problem with my Harmony 360 and Momitsu V880DX DVD player where I couldn't get the DVD player to power on when starting up. The problem only seemed to arise when starting up from a power-off state--the DVD would miss the power-on command and I'd have to re-sync with Help. The problem did not occur when switching activites.

This situation usually indicates a problem with the delays. I tried increasing the Inter-Device delay substantially, with no success. In the process, I discovered what I think is a bug in the Harmony software--very high settings of interdevice delay (above about 4000 ms) seemed to disable the power-on command entirely--not only did it not work when starting an activity, but I couldn't even fix it with help. But it's hard for me to believe that the player really needs such a large interdevice delay, anyway. Working with the original DVD remote, I had no problem getting the DVD player to see a power-on command when delivered right after a command for another device. I also tried increasing the number of repeats to maximum, but that didn't help, either

What I ultimately did that seemed to solve the problem was tell the Harmony software that I needed different commands for on and off (even though the player has no discretes), and define the power-on command as Play followed by PowerToggle. Since the DVD player is off at that point, the initial Play does nothing, but apparently provides whatever little buffer the player needs to be able to see the PowerToggle command.

Did you try increasing the "Power On" delay? Also, by default, a "Watch DVD" activity is set to send the "Play" command at the start of the activity, and to send the "Stop" command on activity exit. These options are under the "Watch DVD" activity > Customize > Change Options.

A long shot (but one which solved a power on problem on an LCD TV for my brother this weekend) is to try relearning the power on command in RAW mode to see if that has any effect.

The wierd thing is that all other uses of the power on command worked fine (using the help and/or the relevent command in Device mode); just the power on via an activity. Like you we initially tried altering the delays (and also the number of repeats) with no success but relearning the command in RAW mode fixed the problem for him.

The Power-On delay is the delay after the power-on command is received, before the Harmony sends other commands for the same device. In this case, the problem was that it wasn't properly receiving the power-on command in the first place, and since my DVD player doesn't have inputs to set, there are no additional commands sent for the device, anyway. I have the Play and Stop commands at activity start disabled; the way I solved the problem was to issue a Play command before the power-on command; since the power is off at that point, it has no effect.

on my mx500, the solution was to send a 'stop' command prior to the 'power' command.
the first command brings the IR sensor to a 'watching' state....

extremely reliable now