I fixed the kernel line and now the MD is booting successfully. If it happens again, I'll know where to look.
Thanks for the help!
I know how it happens officially but something else might cause it as well- basically when you go to the "power" screen of your MD on the orbitor, and the MD is on, there is a button on the top right that has the legend "Restart MD as XXXXX". In my case, the XXXXX is something like "Err parameter not found".
This confused me for a while until I figured out that it is probably getting XXXXX from the MD config - see webadmin for this MD where you specify what the base operating system is for this MD. For all of mine, this field is blank, and that's probably where the "Err parameter not found" message comes from. I presume, but haven't tested, if you fill this in as "Windoze 7" or whatever, then the button will make more sense.
Anyway, it turns out that this button does fubarring of your pxeboot.cfg file and it is an intentional thing- If you choose "Restart as Windoze 7" then it writes the change you saw to the file, and restarts the machine. When the machine comes up, it tries to boot the underlying O/S which doesn't work if you don't have one!
You can test this by viewing the contents of the pxeconfig boot file before and after clicking the above button from an orbiter. You can fix manually, as you did, by editing the file or you should be able to just open another orbiter, point it to the relevant MD's power page and click this button which I guess will read "Restart as LinuxMCE" when the pxeboot cfg file is fubarred.
Does that make sense?
I discovered this over the w/end and meant to document it in the wiki because it had me a wee bit flummoxed too. When I document in the wiki I'll do it from my MCE machine so I can test and be a bit more accurate in my description... this is just from memory.