There is a new low carb website, Authority Nutrition, doing a wonderful series of blog posts explaining in clear simple language many aspects of the diet, the research behind it, and tips to achieve optimal health. His latest is:
The 15 Top reasons you are not losing weight on a low carb diet.
You have likely seen them all, but it is a good list in one short article.
http://authoritynutrition.com/15-re...-low-carb-diet/

Two years ago Mark Sisson had a similar list on his website for Paleo/Primal dieters. 17 Reasons you are not losing weight. Some more tips to consider, no matter what low carb/Paleo/Primal plan you follow:
http://www.marksdailyapple.com/17-r.../#axzz2MbsvHy7z