Hi @KatieStanger,
Can you perhaps post a screenshot of the popup message you're seeing? I'm not familiar with the message and it would help to see the exact wording. Refreshing isn't a term that Canvas generally uses, so my guess is it could be referring to refreshing/reloading the page in your web browser, but I could be totally wrong. Any additional info/screenshots you can provide would be really helpful. If other students are working in the course already, it doesn't seem like there would be an issue with the course itself, so I hope we can help to narrow down the problem with the selected students with the additional info...
I'd also suggest letting your school/institution Canvas team (usually in the eLearning / IT / Digital Education areas) know about the issue, as they may have some local customizations that we in the global community here wouldn't know about.
Hope this helps a bit.
-Chris