When I try to upload datasets I get an error message "Two columns mapped to target column: ptid_full".
I am not sure why this is. "ptid_full" is the subject ID as defined in the Study Properties.
There is a second column in the Excel sheet named "ptid" as you can see in the screen shot. Deleting this column in Excel fixes the problem, but I don't understand why LabKey is trying to map two columns instead of only the "ptid_full" column.
Additional finding-- renaming the column "ptid" to "ptidnum" in Excel (instead of deleting) also allows upload.