Hi - my Mum was a SW consultant for many years and I also followed the diet. Both of us couldn't lose weight following the green plan, I don't know whether we were particularly sensitive to carbs. I put weight on when a followed a whole week on green. It is physically possible to eat too many free foods - losing weight is an equation calories in versus calories used if you eat 2500 calories every day of "free food" but only burn 2000 calories up you will not lose weight.
Most of the free foods are low calorie which means its unlikely you will eat enough to bring your calories to a high enough level to not lose weight but it is possible. Adding in your healthy extras and syns you could easily pack away a lot of calories
e.g. Pasta and Sauce is 300-400 calories per serving,
plus 3 mullerlights at 100 each,
couple of bananas at 100 cals each,
plus 1/2 pint skimmed milk - 100 cals,
bran flakes 100 cals,
1 oz cheese 120 cals,
4 ryvita 120 cals,
jacket potato average 250 cals
can of baked beans 300 cals
100g cottage cheese 90 cals
35g choc - 10 syns 180 cals
Total = 2060-2160 calories if you add in another 3 mullers and another pack of pasta and your totals up at 2660-2760 - nearly 700 calories more than the recommended daily intake just to maintain current weight.
Portion control is still really key - looking back I think I used to overeat my free foods because they were free rather than stopping when I was full and as a result lost weight really slowly, took me 9 months to drop 12 lbs.
Everybody is different and if you can pack away the carbs and still lose it - fab! But not everyone can!
Good luck with your journey
Carol x