Understanding the Limitations of Anonymous Guests
Problem
When learners log in as anonymous guests (e.g. by clicking on a "Log in as guest" button on the login page), they can enter any course that allows guest access. But guests always have read-only access. This means that they cannot:
Sign up for face-to-face sessions
Take quizzes
Fill out feedback surveys
Post in forums / discussion boards
Edit wiki pages
Participate in a chat
Submit assignments
Add glossary or database activity entries or comments
Receive any scores or grades, including in SCORM files
Note that the list above is not an exhaustive list. Basically, any activity that requires a guest to participate in will either not work or will work with severe limitations.
So while this feature can be handy when you want to let a user simply look around at your work or perhaps see a course before they decide to enroll and/or pay for the course, it's not useful if you need to track someone's participation or progress, or if you need them to participate in the course.
Solution
The best solution is to create an account even for guest users. This can be done by enabling self-registration on the site, or by manually creating the accounts for your guests - assuming you know who they are.