Creditor Transaction batches will error with "Conversion from string %s to type decimal is not valid"

If the creditor transaction batch number of a saved batch contains non-numeric characters then this error will occur.

It is caused by the attempt to check if the Invoice number of any lines on the batch has already been used for the creditor. If there are, then the attempt to convert the batch number to decimal to display the message to the user causes the error.

Work-around is to turn off the system setting "WarnOfDuplicateInvoiceNumbers" under the Creditor tab of System Configuration.