I'm sorry to hear this is happening! I would suggest clearing your cache and cookies, and looking again. Does it happen when clicking on something specific, or any item? Depending on the if the course is still active it could give an error.
I would follow our guide for How do I clear my browser cache on a PC? will walk you through the steps for this. You might want to reach out to Canvas Support if you continue seeing this error.
Let us know if you have any other questions or concerns!