1: It's a 120-ohm resistor, not a 430. Might help if you have the right hardware.
Have you tried moving some of them around(the Martins) or at least changing the order they are connected in? Might not be possible. Are they all set up the same? Are they properly "zero'd" so you know where they should be oriented by default?
And yes, you NEED to really use DMX cabling.
2:
What version of MyDMX are you running? Use the latest from the web site. I would assume you're runing XP(which after my Windows 7 experience, I can't find any reason to switch to anything past XP, Vista sucks and Win 7 sucks differently).
You'll want to select ALL your fixtures to make the scene generator work on all of them especially if you've given all the fixtures different addresses. When I make a circle with my movers and I want 20 points, I only get 6 steps. Go figure.
I think you have some other issue that you haven't shared with us yet, bt I think that may be because you don't have all the information yet.
Thinks are pointing to bad cabling and bad terminator. Plus one more thing I mention next:
ALSO, considering getting an Elation Opto Branch/4. It will boost your signal as the MyDMX dongle's signal isn't as strong as your controller. That could be key as well as it is getting obvious that your signal strength is faltering the further out you go.