Ive searched for this but only found references to a “snapshot” I’m new to UEFN, and this is my very first project and its not going well, whenever I try to create a simple map I get the follow error
Thank you for your report! We would like to look into this further, would you be able to submit a bug report using the form available here: Fortnite Creative
I don’t know if this was ever solved but what fixed it for me was to run “Verify” in the Epic Game Launcher for UEFN and Fortnite. Next time I started it up it worked.
I am having the same problem, but the verify method is not working for me. 
Hello,
Could you please start a new thread if you are still having this issue? We’ll need to have your latest information to investigate. Thank you!