Can't you compare the file to the exception file to find the rows. In my experience truncation errors may be thrown when the flat file connection manager has the column defined too short. Define each column length in the connection manager too match the destination. Another approach is the create a staging table with an identity column and single wide column for the file rows, load all the columns with delimiters into the one column and load from there where you will get a truncation error if data is longer than the destination table.