Hi Stephen,
First, thanks for the question and reply.
I have resolved this problem by not using that particular method of uploading grades and feedback commentary. Since that strategy (ie, using the downloaded XL worksheet) seems to be limited by not accepting the username field and restricting to only comma separated values, I instead use the general import tab via the gradebook. This works for me.
So, to your question, I would only get an error when I tried using a field other than the prescripted "Participant" + a whole number approach as the key field.
I do have a follow-on question that I may need to post as a new item though: is there a place where the maximum number of chars is set that will go into a comment field, or is this a field that must be restricted in size for other reasons?
I either want to change the maximum allowable or to know the limit. If you happen to know this, please let me know.
Again, thanks for your support.
-George