Unfortunately, the Dutch rail system is not very user-friendly for foreigners.
In Rotterdam we tried to buy our tickets to Amsterdam via the "self-serve" machine outside the station. We found out that not only does it not take international credit cards, but it also does NOT accept Euro bills.
The total cost for 2 tickets was 28 Euros. Rather than letting me put in three 10 Euro bills (and giving me back 2 Euros for change) I had to go to a nearby casino, exchange my money for 1-Euro coins, and then put 28 coins into the machine to get our tickets. Completely ridiculous!
So, if you intend to buy rail tickets in the Netherlands, apparently the only way to do so is with a Dutch account or coins!