MSpice asks:

I know there are rules regarding contribution limits and time periods for making contributions - but are there also IRS rules for how you invest the money once it's already in your account?

I think the person with whom you spoke was confused about what you were attempting to do. Once the money is inside the IRA, there is no IRS rule that says you must identify what year's contribution is being used for the investment. Evidently, Buyand Hold.com's procedures online can't handle a monthly investment that uses funds already in the IRA. My guess is the system thinks the money is coming from a monthly deposit/contribution you are setting up. Try calling them again, and this time ask to speak with a supervisor.

Regards..Pixy