If you have issues accessing a program, a firewall may be blocking access to the site. Check with your IT department to see if they can resolve the issue. You can test your network access at: perts.net/network-test.
Some additions solutions are:
Confirm the participant's Roster ID matches the one in the Class' Roster
Confirm the participant has the correct participation code (3-4 characters)
Suggest the participant take the survey in an incognito window, another browser, or another internet connected device (tablet, laptop, computer)