• Log out of ALL Google accounts on the browser and log in to ONLY your school Google account. 
• Clear cache and cookies on your browser (instructions for Chrome) 
• Close and re-open your browser
• Try an incognito window in Chrome
• Try a different browser (Chrome, Firefox, etc.) 
• Restart your device
• Try a different device (computer, tablet, phone, etc.) 
• Try turning off ALL of your extensions in Chrome (on the right side of the address bar) and then turning them back on one at a time to see if one of them is causing the issue.
  

Second set of troubleshooting steps:

1. Open drive.google.com
   
2. Make sure you are logged into the SAME account as your Google Classroom Instructor account
   
3. Click in the Search field at the top and type in the Student's name as it appears in the Google Classroom assignment
   
4. A list of files submitted by that student will appear
   
5. Check the "Owner" column - each file SHOULD have the Student's name in the "Owner" column
   
6. If a file has "Me" listed, this file will throw an error when the associated Assignment is Returned
   
7. Right-Click on each file with the wrong permission, and select "Share"
   
8. Next to the Student's name, you should see the word "Viewer" - click that and change it to "Owner"
   
9. Follow the prompts to make the change final
   
10. Repeat for each file with the wrong permission
    
11. Return to Google Classroom and Return Assignments as usual