A possible cause of this error is a reserved character in the Description field of a transaction, for example a | (Pipe) character. Check your transactions and remove this or amend to something else.
The problem probably does not affect all of the items in the transactions being processed and so, to isolate the offending item, this can be done by testing a decreasing number of the items in the selection until the offending one(s) are found and then checking the transaction for unexpected characters as below:
Deselect about half of the transactions to be processed and click Process. If the Process Remittance BACS pop-up appears then these have passed validation. These items can be processed if required, or the screen closed using the x option in the top right corner of the pop-up.
If the error message still appears then reduce the selection again and retry. Continue until the cause of the error is identified.
Once the culprit(s) have been identified, use the Purchase Transactions Enquiry screen to check for unexpected characters - specifically in the Header Reference and Description fields.
If this has been done and you still cannot run your remittances then Support will need to run some scripts on the database. Therefore please raise a new case online and reference the title of this article and please include details of the transactions affected.