Do you have a Visual Studio Solution with your uproject file in the project folder? If so, try right-clicking on the uproject and select generate Visual Studio Project files, allow to compile, then try opening your project in UE4.12.3.
If not, try opening a version of your project in UE4.11.2 First (since you can’t go back to 4.12.0). Work out any problems, then update that project to UE4.12.3.
I regenerated the VS project files. It did not offer compilation so I opened the project in VS and rebuilt it which was successful.Sadly the project still doesn’t load.
Took old 4.10 version, upgraded to 4.11.2. There were no problems to work out, the class mentioned in the error message compiles fine. Tried to upgrade to 4.12.3, not loading, same error as before.
Upon further closer examination, it looks like the specific asset: D:/Projects/DroneAlone/Content/System/Blueprints/Missions/BaseMission.uasset is the source of the crash. Try removing this before updating to UE4.12 and, if successful, remake this in UE4.12.
While my last post may help in getting around this issue, it turns out this is a recent bug in UE4.12.3 and has been reported as UE-32356. I’ve made a note to update this post once it has been resolved.
The BaseMission class is a fundamental part of the project. Removing all references to it and its child classes then redoing everything would take weeks of work. And even if I fix this particular class this way there is no guarantee that another class (not yet reached due to the crash) won’t die the same way. (Been there, done that.)
Is 4.12.2 available in any shape or form? I checked Github but only saw the 4.12 branch which I assume is 4.12.3 by now.
Oh I found the 4.12.2 source on Github. In case someone else is looking for minor-minor versions: https://github.com/EpicGames/UnrealEngine/releases
I’ll stay with this one until the issue gets resolved.
I’m facing the same error with UE4.12.5.
I know the asset cause the error but that is like PlayerCharacterBP.
I don’t want to delete it.
Crash is caused when the engine open the asset before user do.
evadable,not so fatal.but,
crash,crash,crash,
4.12 is full of error. I cannot work with this.
This bug has been reported and is being worked on. In the meantime, the following might help the issue and will not hurt your project: Right-Click on the Contents folder in the Content Browser and select “fix up redirectors in folder” and Save All. In the toolbar, click the down arrow in the “Build” button, scroll down and select “Map Check” -correct all errors. Save all and close. In the project folder, delete the Intermediate and Saved folders. Reopen project and see if it still has this crash. If so, delete the Config folder but this will result in having to re-enter your Project and Editor Settings.
If these steps do not help, I recommend working in an earlier version of the Engine until this bug has been fixed.
I resolved this.
In my case,the cause is duplication of Interface.
I tested with a blank project.
I created ActorBP, InterfaceBP ,a function of it and duplicated the Interface.
I tried to introduce two Interfaces into actorBP.but it was rejected.
so I changed the function name of duplicated interface.
two Interfaces were introduced well.
This actor causes this error.
If this actor is placed in starting level,
Engine crashes when initial loading completed.
If this actor is PlayerBP like me,
crash caused when PIE started.
If you open the BP before engine open it,
the crash will never happen.