I did the 2007 C2C crossing and reached only as far as Kirkby Stephen, not blister's or lack of fitness, but a gammy knee joint and it was painful.
However, I blamed a couple of factors for that, lack of training and weight of ruck-sack, I was camping. I learned my lesson since then and in 2009, did the whole walk, no problems, did plenty of training and reduced the weight and I was camping. But, this time, it was the blister's being the bug-bear and this was due to cheap walking boots.
This year, I'm doing the C2C again and will be my C2C walk, thank god. But, I'm doing a mix of accommodation and will be going super-weight.