Forbidden messages appear when a user's IP address is not remaining consistent throughout the course, or the LMS security protocol has been compromised in some way while accessing the course. Some causes of this are listed below:
If you have more than one online course open at the same time. Close one or both courses, and try to restart them, one at a time.
A user's IP address may not be staying consistent while they take the online course; switching computers or locations may help to keep this from continuing.
Your browser's cookies need to be on to verify authorization to access online courses. If your browser's cookies are turned off, they should be turned on in order for you to access courses. You can learn about troubleshooting cookies in your browser here.