I’m getting an error when i changed the engine version that i’m using. I went from 4.10 to 4.12. When i tried to package the project i received this error message.
Some deprecated warning and then some other stuff that i don’t know what is happening. Can someone help out?
Clean up and rebuild your project
You’ve got linker errors because your compiler is unable to match the function declarations in your header file with the function implementations in your cpp file. It’s telling you which functions it can’t find. You should clean your project and rebuild it, and if the errors are still there, you should look through your source code for the missing function implementations.
The deprecation warnings are detailed in the documentation and the updates have been posted in the forums. Just do a quick search for them.
So just right clicking on my project pressing clean then build? I’ll try doing that, those functions i do not use nor do i ever heard of them. so implementation of some i did not even write? =/
Yeah, that’s one method to clean your project. However, be warned that if you built the engine from source, it’s going to clean ALL of the projects in the solution. When you rebuild, it’s going to recompile everything and it’ll take you something like 45-60 minutes to rebuild it all.
What you’re really trying to do when you “clean” a project is delete all of the intermediate .OBJ files, which are sort of like partial binary data objects created by the compiler. Usually when you run your project, the compiler is pretty good at figuring out which header files were modified and it recreates only the OBJ files it has marked as “dirty”. Sometimes, the compiler messes up and you’ve got an outdated OBJ file that needs to be rebuilt but it doesn’t know it. So, you just ask it to rebuild all of the project OBJ files. Think of it kind of like refreshing the cache on your browser. Anyway, enough background…
The fastest way to clean your OBJ files is to go into your project folder and delete the intermediate folder. Then right click on your .uproject file and select “generate project files”, reopen the project in visual studio, then press “F5” or build and you’ll be back in business in 2 minutes.
Cleaning didn’t fix it. I believe they may have changed something with the base class or some parent. I deleted all my behaviour trees and will recreate them from scratch again. I’ll mark as solved because the error is not an issue anymore.
Thanks guys for all the help! 
I have seen these issues already, they are also stated in the threads below and how to solve those issues.