Some plugin authors have attempted to implement a pseudo foreign currency implementation in the cash book, but are blocked by a check enforcing the debtor / creditor to have a currency to be the same as the bank ledger currency - "Unable to set DebtorCreditorAccountID - the Currency used differs to tha bank currency." (sic) is the current message presented.

Add a system setting - which when set will bypass the current enforcement preventing the currency of cash book transactions to be manipulated by plugins.