I’m seeing an error message that says the ebook is locked/being used by another person. What does this mean?

For licensing reasons, some ebooks can only be used by a set number of people at the same time. If too many people try to access these ebooks simultaneously, the last person to open the ebook will see a message telling them it is currently in use. You will then need to wait for the first person to stop using it, before you can access it.