If you see a red unlock in the User Activity Log, it will also show an error code.
Click on the orange icon in the ERROR column to open the User Activity Error Code Guide.
This guide will help you identify many of your end user issues and provide a suggested action for each code.
Keep in mind, your organization selected Vitrium to control access to your content so many of the errors are situations where the user has reached or exceeded some limit you have set in your DRM policy.