I would try:

 = SQLSETPROP(lnConnHandle, 'Transactions', 2)  && Manual transactions
= SQLEXEC(lnConnHandle, "INSERT INTO CUSTOMER (Customer_id, Barcode...); 
	   	 VALUES (?m.nTOTCUST, ?m.cBarcode...)")
= SQLDISCONNECT(lnConnHandle)

Other way is to remove inserted fields one by one to find which caused the problem.