Error APP-FND-00531 occurs when contract number is changed on Pricing Rules tab

We have Coverage Templates set up for various warranties we offer. These Coverage Templates are associated with the customer's contract. On occasion, the wrong Coverage comes up in the Pricing Rules tab under Charges in the Service Request. When this happens, the user changes the Contract Number to associate the line with the correct Coverage. This is where the error comes up. Once the Contract Number is changed to reflect the correct Coverage Template, the Billing Currency which usually says USD dissappears and these errors pop up: 'Currency formatting cannot be performed without a currency code' and 'APP-FND-00531: The amount could not be correctly formatted. The correct format is 9999 or -9999.'. Service Profile "Charge: Default Price List" is set to our primary USD price list, "Currency:Mixed Currency Precision" matches what is set up in Receivables Manager and "Service: Charge Line Default Price List" is set to 'Use value from profile 'Charge Default Price List'. Precision for currencies is set up correctly in General Ledger. Any ideas what could be causing this?