Hi Ivana,
Are you using the download worksheet approach? Because if you are, I had to give up on it because that approach seems to force you into using a set of key field identifiers to associate which user belongs to which grade record - it uses the funky "Participant" plus a number. Those identifiers are not permanent, so I need to use something like the username field.
Because of that matching problem, I found a work around because I do all my grading offline using some sophisticated spreadsheets I've developed over a couple of years. I need to do it this way because I'm looking to develop a student performance dashboard prototype that could be used to direct improvements based on different learning analytics I collect that Moodle does not.
My workaround is to do it this way...
1. Use the course admin interface and select Grades
2. Use the Import tab, and I save my Excel grading worksheets as Tab delimited, and in this import window, you can select Tab as the delimiter.
3. In the upload window, I match what I have in my grading worksheet for Username with the Moodle equivalent of username to set the key fields.
4. Then in the same window below the key field, I set my grade fields with the appropriate assignment number and for the feedback I use my field with Moodle's comment field for the same assignment.
Hope this helps your situation. It's a bit frustrating getting help in here at times. And I don't know how to get the download worksheet approach changed so that you can use different fields for the key field instead of the temporary identifier used now.
-George