Alathea is right, I've made a mistake in the chart on the larger size. I did notice this actually when I was knitting the small test of hte larger sock and I'm so cross with myself for forgetting to alter it.
The mistake is in the first two columns on the chart (ie the first two stitches) which should be swapped around - correct pattern should read 'p1, m1(or m1 purlwise depending on which row your on). I've corrected the chart and if anyone wants a new copy please e-mail me.
I'm so so sorry about this.
THIS IS ONLY APPLICABLE TO THE LARGER SIZE THOUGH.