If you cannot open a course or single course elements it may be that the course author has not given you the relevant rights or the course is being updated at that very moment.
Given the case that you have just found an interesting course and want to get to the course view. If you are notified that you do not have enough rights to launch that course this means that the course is restricted to a certain group or to a certain period of time. A course may could also be have been password protected in an earlier OpenOLAT version, which allows authors to restrict course access independently of groups or time.
Perhaps you have been able to launch a course but later on you get an error message telling you that its authorization has been changed. This means that the course author has restricted the access in the meantime or closed that course.
If the course author changes the password at a later date, all users must re-enter the password.
In all cases please contact the course author to grant you access.