I had a similar situation. During the interview process, my current position’s primary focus was finding a leader in the implementation of an enterprise-wide CMS. While I didn’t have direct experience with the CMS that has been chosen, I had 5+ years of experience in developing a content management system and integrating with others.

I was able to use the knowledge I have gained from my past experiences and while I wasn’t able to always address the CMS-specific questions, I was able to talk about best practices and learned experiences.

The thing to remember about an ERP system is that it already has a large number of capabilities built into it. Unless your organization derives a significant competitive advantage from your existing ways of running HR, Finance, etc., or you exist in an industry with unique regulatory requirements, you shouldn’t try and replace the existing functionality with something custom to you. Revisiting all those decisions will dramatically increase the cost of both implementation and maintenance (because you won’t easily be able to accept any new features without customizing them).

In this situation, a big chunk of your role as a BA is to help the organization change its processes and operations to bring them into line with the application. You really can do that a lot better if you understand the capabilities and limitations it already has.