you have to adapt your business processes to the ERP system, not the other way around
I hear this all the time, and I'm not convinced. Companies buy stuff. They either sell it, or use it to make something and then they sell that. They either make it when somebody orders it, or they make it in advance based on forecasts and keep it until somebody buys it. They send invoices to customers, they get invoices from suppliers. The invoices can go before the goods, or after...
All that's there, in the standard.
I think that 99% of the time when people say it doesn't support their business processes there's an implied "in exactly the same way we did it before, down to the tiniest detail including the colour of the post-it notes that you stick on Maisie's screen when there's a goods return."