AAI set up for Business Unit

Hello we have several business units or "sub-companies" that we are attempting to set up AAI for PC (Trade Accounts Payable) and RC (Accounts Receivable) however we get an error message that says that it is a duplicate since the Company is the same for all business units. Is it not possible to set up AAI's for business units?

For example:

Accepted -

Item Number = RCDA

Company = 01414

System = 3B

Business Unit = 1414-A

Object account = 64999

Not accepted -

Item Number = RCDA

Company = 01414

System = 3B

Business Unit = 1414-B

Object account = 64999