Hello! I’m using google translate because I speak Spanish but I couldn’t help but see that you have the same problem as me.
I also had this problem and the way I solved it (for now) is when opening a new session, when the error appears, open in the upper left part of the editor “window”, then “output log” and you will look for an error line similar to this (example):
LogValkyrieValidation: Display: Found disallowed objects for asset Content/ExternalActors/Name of your project/9/CT/YSS47N9PFK2ZMVEBSSPXGZ.uasset
In your case, the number “T/YSS47N9PFK2ZMVEBSSPXGZ” may be completely different.
you are going to copy those numbers and characters (T/YSS47N9PFK2ZMVEBSSPXGZ, example)
and you are going to paste it in the search engine of the window called “outliner” (the one that is to the right of the editor)
It will show you the object that is causing the problem. In this case, what I did was delete it and it solved my problem.
I ran into the exact same issue when going through the “Your First Hour in UEFN” tutorial. It seems that it won’t launch if you include the Niagara System VFX content that was added in the earlier section of the tutorial. They can exist in the project, but not the scene.
We are taking a look at this.
Its happening to me too, Found disallowed object type /Game/Sounds/Apollo/Biomes/PA_Announcements/BP_Audio_PA_Actor.BP_Audio_PA_Actor_C . I cant launch the session because of that.
Same issue. When can we expect a fix?
Same here, Glad to see people have stumbled across this. It seems the tutorial was written then a handful of things changed. Hopefully this is a minor adjustment.
If you are getting this while trying to do the “First Hour in UEFN” tutorial, you can get passed it by deleting the Niagara Component from your “Prop_Barrel” blueprint.
@mhughson thanks for the workaround. For everyone here this should unblock you. We’re currently investigating why these assets don’t pass validation. Thanks for your patience.
Hello,
I’m having the same error after migrating a map I did on another project, I fixed blueprints and other things that were not compatible with the project, but I have this error left that prevent me to start the session:
" LogValkyrieValidation: Error: [16] Found disallowed object type /Script/NavigationSystem.NavigationSystemV1 "
I tried few steps to search for the error, make sure it wasn’t something on the map or on the project but it isn’t something I can delete, so I am stuck with that error 
If you know a fix, i’d be very happy 
Thank you very much, this solution worked for me! 
I’m getting this error: LogValkyrieValidation: Display: Found disallowed objects /Script/Engine.LevelScriptBlueprint
LogValkyrieValidation: Error: [16] Found disallowed object type /Script/Engine.LevelScriptBlueprint
For me it says /Game/Athena/Items/Cosmetics/Sprays/SPID_074_CuddleHula.SPID_074_CuddleHula
/Game/Athena/Items/Cosmetics/Sprays/SPID_024_Boogie.SPID_024_Boogie
They are both sprays but I don’t see them in the map where I put them.
Made some more test and it seems that it was the map itself that was the issue, launching session is working after deleting the map.
It’s a bug tho, because there was nothing particular in the map (only meshes and pointlight was remaning after I deleted everything that couldn’t validate assets).
Edit: I tried importing my files again and just deleting the map, and it wasn’t enough, I had to delete my materials too and that fixed the issue, I was able to reimport it the “normal way” (Importing the .png files and not the .uasset from another project folder)
@HalcyonKnight96 Is there a way to be notified when a fix has been implemented? Or do you have a timeline?
Hey, can u explain more how
u can fix it? I have same the problem. 
