Something went wrong. Unit was not saved!

Hi,

I have CoursePress installed, but can't seem to get it online.
Whenever I try to do something with a unit, it fails. Mostly it is "Something went wrong. Unit was not saved!", but previews also don't work. Next to that getting the unit live is also impossible.
Could you please help me out with this? I'm a starting business and I need to get these courses online...
I read somewhere that the PUT has to be changed (no idea what that means) and that there is a hotfix zip file (which I can't find).
I have granted you access to my website through the wpmu dashboard.

Thank you for your time.
Maurits