Hi Mark,
Even though the message says Id, the header in the input file is ID and the column in the vendor reference data is ID. I just double checked both places and tried again. Here's what I have learned:
If I add a column called Vendor ID, change the header in the source file to Vendor ID and delete the existing column called ID it works.
I also thought maybe there was something wrong with the values in the ID in the source file, even though they haven't changed much. I changed them all to a random word and tried. Same error.
It gives me the impression that all of a sudden there is something about a column called ID that is causing a conflict ?
George