"Some error or other" isn't really very helpful. I had a play with that script, and it worked fine once I replaced all the < entries with the less than sign (<) - < is what you put in web page source code to create a <, since < is a reserved character in html.
Anyway, to get that script to do anything I had to assign all 12 vehicles to the same squad and place them in column formation.. so that kind of defeats the purpose of using it to avoid having them all in the same group.
You might know this stuff but:
1) All wheeled vehicles in OFP will follow roads to their destinations if they can. The system OFP uses for finding the best path takes surfaces into account. Plonk a jeep at Vernon and a waypoint at Lamentin (eg), then moveInCargo yourself to see it work. The jeep will drive all the way there on the road (though they do sometimes hit trees etc.. I wouldn't give the AI a driver's license)
2) Tracked vehicles will go wherever the hell they feel like, and there's not a lot you can do about it.. I've tried. The best you can do to include tracked vehicles is to put the leader in a soft vehicle, and with column formation they at least go *close* to on the road.
3) All units in a squad will wait for other units if set to 'normal' speed mode. They usually hold a distance of about 20-30 meters for soft vehicles like jeeps or trucks, a little more for armoured vehicles.. it depends. So, if you try the trick in (1) with four or five jeeps / trucks in the group, set them to column formation and normal or limited speed, they will all drive all the way in formation, and will automatically wait for each other.
So I don't really know what that script is meant to achieve... it contains no system for moving the cars that I can see, just for telling them to wait for the one behind if it's lagging. You'd need a ton of waypoints to make this work to get what you want.
If the order of the vehicles is desperately important, then create them in the editor as being in their own groups, then add them to the group of the first vehicle in the order you want them to be in using the join command in a script. Whatever order you add them in will be the order of the column.
IE: when you want to make the convoy, put them all into that group, then when you get there, split them apart again.
The only other way to do it is some kind of _car1 domove (getpos _car2); _car2 domove (getpos _car3... etc etc in there as well, but a scripting solution will have to be pretty well written to cope with all the possible problems.. like.. what if one vehicle gets destroyed? Or damaged? Now all of a sudden you've got a guy on foot, so the whole convoy goes at his speed..
Basically, my advice would be to use the built-in stuff for group manuvering. It may suck, but it's a hell of a lot easier than coding an alternative yourself. Try and work with the game's systems, rather than against them.. it's a lot easier, and OFP copes better.
Cheers
CareyBear