This is potentially an issue with the BBB servers. Test in another browser and then if still having the same issue, do the following:
- Edit the class
- Add a new session for the same time
- Delete the old session
- Save the class
- Inform all the participants by sending them a message to enter the new session that was created
**If any of the above problems persist, have them restart their computer. Make sure to have them test and exhaust all possibilities that might be causing the error.