@seekborrow Hi, if you've tried all the steps above but the error message "another canvas is already open" still shows on myViewBoard Classroom, please do one more try:
use another browser and launch myViewBoard Classroom through https://myviewboard.com/home.

If there's an opened canvas, you can close the previous session and restart a new one through the warning message.

If it's still not working, please provide the following:

• time of the error
• device brand and model/ operating system details
• browser name and version

This would help us investigate and resolve the issue. Thank you.