One of the main point which results ERP implementation failure is less product knowledge. Less product knowledge creates the following problems:
1. So when you have less product knowledge , you will mostly rely on customized solutions rather then standard processes which are already in the system. More customization in ERP sometimes creates frustrations and failures because of less testing and quality assurance.
2. Sometimes you give deadlines in pressure and to please the clients . This leads to miscommitment and later destroys the trust. Being a ERP vendor , you should commit what you can deliver. Remember trust is the key to success in every manner of life.
3. User acceptance is the key in successful delivery. Proper delivery of manuals and proper practice sessions for user needs to gain trust and interest in the system. ERP implementation is not normal as other IT deployments , its not like that . Most IT applications covers only some certain tasks, but ERP covers everything in the legal entity . from SCM to HR , you need to provide system for every process . Sometimes users also do not want to shift from their legacy ERP to the new system. Being an implementer, you need to check users mood swings also.
4. Commonly you need to align system with business processes of the company, but sometimes you need to align business process with the system. It means you need to tell your client , if you adopt this change in business process this will create more robustness and traceability.
So before implementing ERP , you need to implement trust. If you gain trust the client will tell you the operations clearly and you can implement with good deadlines and timelines. Btw many reasons are their for ERP failure, but according to me these are common.