Check the following: 

• Is the domain expired or inactive?
• Has the course already been added? In rare cases, particularly if there are multiple courses with the same name and information, it can look like a course hasn't been added when in reality it has already been created.
• Check where the course should be added - if you are in a top-domain setup, the course must be added in the top domain.
• Check that the person adding the course has the necessary permissions - normal users cannot add a course.

If none of these are the cause of the issue or you get an error message, contact Support for assistance.