I saved a project this morning, then I come home to open it again only to find thar error message
@Spider-Man Thank you for your report! Can you please re-post using the “New Issue” option on the Issues and Bug Reporting forums? Posts with this feature are connected directly into our development team so we can quickly get to them!For more information, such as how to get the reference ID, please check out the article here: https://create.fortnite.com/news/using-the-creative-and-uefn-bug-reporting-form
Hey Spider-Man,
Does it give any other information why ?
Post a screeny of the error message.

I was given this error in specific
Haven’t seen that one before, hopefully someone can help.
Have you tried loading another project, then reload this one ?
Do you remember the last things you did ?
Maybe with the editor not running, move your Big project folder to somewhere else on your computer out of the Fortnite Projects, then load up UEFN and redownload the project from the servers, this all depends on the last time you backed up.