Cannot select Bank at supplier header or site levels in R12

Hello,

We are testing R12.1.3 and are having issues attaching banks to suppliers and sites. When we setup a new supplier and click on the Banking Details tab, we cannot pull up any Internal or External banks for either the supplier or the site. If we choose create and select Existing Bank, we can pull up the bank we want, but when I save, it says "The external bank account already exists". Has anyone else come across this issue? I have an open SR that I'm waiting for help on.

Thank you,

Christine