I'm currently reading Ina May's Guide to Childbirth. She actually discusses common reasons why women have problems in labour & birth and how often there is a misdiagnosis - including CPD. It's all about the support and environment created by the caregivers and support people. I'm not saying this is necessarily the case for you, but it might be worth having a think about it.
Really brilliant book, btw, worth a read.
All the best for your VBAC