A few different things can cause this error. The most common being:
1 – Not publishing as SCORM, AICC, xAPI, or cmi5 in your authoring tool. If you’re unsure of whether your course is published to a certain standard, here are some files for you to look for. These specific items need to be in the root of the package for each standard.
SCORM – imsmanifest.xml
AICC – A file that has the extension “.au. For example “course.au”.
xAPI – Technically anything can be xAPI, but most authoring tools will include a tincan.xml.
3 - The course is over 100MB (expanded) and you're on a Trial account.
If you have any questions, please send a message to firstname.lastname@example.org.