I had the same issue last week. I exported the entire BR_Transaction file to Excel and found a date field formatted with 2180228. Once I changed it to 20180228, the error went away. The source was from AP, so I had to change the date field from the source record in the AP_CheckHistoryHeader, AP_OpenInvoice and AP_TransactionPaymentHistory. This customer is on Sage 100 2017 Standard with PU3.