Thanks guys - I've cracked it and it seems obvious now, but I'll explain what I did, so that it might help other modders not make the same mistake as me!!!
I'd made some changes to some of the other data files (soldiers, teams & weapons). All these files I modded through Excel, using the conversion via delimited text files, etc, as you do when working from the downloadable workbook.
I automatically did the same for the Campaign.txt file, so when I took on board yours and Steve's comments, I checked what I was saving into my modded file and then reopened it and there were no additonal " " marks...
This puzzled me - how were you seeing " " marks that I wasn't???
Then it occurred to me to open my modded Campaign.txt file in text (rather then excel) and there were all the additional " " marks plainly visible!
So, simple! I just went back to the original txt file, opened it in text, modded and saved it in text and it worked first time!
The only thing this doesn't answer is why excel puts the additional " " marks in the campaign file, but not in, say, a modded AlsTeams.txt file. But doesn't really matter if you know which to use...
Thanks again - easy when you know how...
Is there any guide that covers do's and don'ts like that?
Also, is there any Q & A guide for beginner modders for doing certain things, eg, if you want to make hedges impassable, open this file and change these columns (something I'm not sure on) or if you want to change the armour thickness of a vehicle, open this and do this (which I can do), etc, etc.