I believe the adobe dng converter only converts camera raw files to the dng format.
Doesn't work with tif or jpeg files, so it seems that's the reason for the "There was an error parsing the file" message.
I can see how my screen shot gives the impression that all *.ARW files were converted, but I don't think they were.
I've closed the window now (and there's no log) and am running the converter on another large folder. I'll let you know if I get any errors from ARW files.
The next batch has finished. I believe you are correct. Thanks for the help!