Supplier Bank Error

1. We created a new Vendor with 2 Sites. Each Site has been assigned to 2 OU's (1 in USA and other in Canada)

2. We are trying to add/create Supplier Bank Details at Canada Supplier Site Level.

3. After adding the Bank Details and when we hit Save/Apply button we get the below error:

     1. The external Bank account already exists   

     2. One of the assignment of this bank account is related to operating unit (US OU)

How do we fix this issue ? We are trying to add Bank Details at Supplier Site level for Canada OU.

I don't see any Banks existing/created under US OU.