While I don't have hard data on this (and it would be hard to establish causality anyway), most of the ERP implementation failures I've witnessed and know about stem from line of business people who firmly believe their company's processes - e.g. collection, billing, etc - are very special and unique, when it is very rarely the case; and when it is, it shouldn't be, the process is likely overly complex due to inertia or lack of will/skills to improve or just legacy. Then, the customizations that need to be implemented to support the "special and unique processes" are so complex that the project's schedule and budget inevitably explode...
ERP implementations could actually be seen as a great opportunity to revisit, optimize and document current processes before the ERP is implemented...