Just after I try to launch a session and get the error, these changes appear in the check-in, even though I haven’t made any modifications to the project. This happens right after I attempt to launch the session. Maybe this could help you track the bug.
Edit: Also if after this I revert the changes, I can launch session normally without getting any validation errors
Hello,
Any updates on this issue?
I’m still investigating on my end to try unblock my project, and I found a new piece of information.
The last version of my island uploaded to the server was version 3880 (I found this in the project size window, the date and time match with the last session I was able to launch).
However, when I start a new session, the version created in the sys folder is 3873.
I’m not entirely sure how the session cooking process works, but could this mismatch be causing the issue?
I solved this issue by deleting the Verse files from the public folder.
They’re not in the same location, but it’s easy to find. I deleted them and then immediately uploaded a public version and published it, and that fixed the error.
It happened to me twice, and I told someone else to do the same and it worked for them too.
I hope this helps.
Hello,
@Flak, still no update on this issue?
This is becoming critical for us, our game is broken after the 36.00 update, and we can’t fix it because we’re unable to build!
I’ve seen other posts on the forum about similar problems, it looks like more and more people are experiencing the same issue.
Hi, thank you for this solution, I will try it now
What is the path of the public folder? it’s located inside the sys folder?
Thank you, I tried that friday, but it didn’t work.
And now, I have an other error, and no sys folder generated, so I can’t retry
Have you added an asset with a strange character? That might be your problem now.
I’ll double-check, but the project was working before. After the update, it stopped working and I didn’t change anything in between.
That happened to me and I followed the previous steps and it worked. I hope you get lucky and solve it quickly 
@nicoplv Sorry that you’re hitting this issue. Unfortunately this is not something that you can work around locally.
We’ve identified the regression here related to backwards compatibility checking, and we are currently in the middle of testing a fix that will solve the issue. Once that’s deployed, an update will be posted to this thread.
Is this something that would be a hotfix or would we have to wait until next patch?
Thank you for the answer, I wait your update
An update has been deployed to our backend that should address this issue; bear in mind that as part of this, local backwards compatibility checking has been temporarily disabled in the editor (it will still be run in the backend when you attempt to publish your project). It will be re-enabled in a future upcoming patch.
Awesome news, thank you @sonictke !!
Thank you! It looks like it’s partially working, I’m able to launch a session, but it never fully starts.
In UEFN, the session stays stuck in the loading phase indefinitely, and in Fortnite, my character remains in the white hexagonal room but on the top left corner it shows “Edit Mode - Up to Date.”
Here is the logs of uefn.
I get a message “Failed to request content update” in a popup but nothing else to understand what’s happening
UnrealEditorFortnite.log (2.0 MB)
Hi @nicoplv
I’ve identified the issue with your failed cook.
If you remove the line
using {UMG}
in your script, does it resolve the issue?
I’m curious if you also tried restarting the editor and re-loading the project with that line in place - does the editor prompt you about any Verse compilation errors?