The message indicates that the device you are working on does not have enough memory capacity to open the lesson file.
- On which device are you working? The memory is different on each device. We advise you to check if the file opens on another device with more memory.
- How large is your lesson file? This is not just the number of pages, but also the number of objects on a page. It may be an option to split your lesson file into several small files.