Update ThirdParty dll

I’m linking in a dll in c++ though edits in MyProject.Build.cs. I ended up with this though looking at various posts here:

PublicAdditionalLibraries.Add(Path.Combine(PathToThirdPartyLibrariesFolder, "MyLinkedLibrary.lib"));
CopyToBinaries(@"ThirdParty\MyLinkedLibrary\Libraries\MyLinkedLibrary.dll", Target);
RuntimeDependencies.Add(new RuntimeDependency("$(ProjectDir)/Binaries/Win64/MyLinkedLibrary.dll"));
PublicIncludePaths.Add(Path.Combine(PathToThirdPartyFolder, "MyLinkedLibrary", "Includes"));

and it works great.
However, I tried to add a new function to my linked library :

int MyNamespace::TestFunction() const
{
	return 4;
}

which is pretty simple compared to other functions I have successfully exported. Now, however, when I try to run game and/or Editor from VisualStudio I get error

The procedure entry point ?TestFunction@MyObject@MyNamespace@QEBAHXZ could not be located in the dynamic link library C:.…\Binaries\Win64\UE4Editor-MyProject.dll

Note that MyProject compiles in Visual Studio.
MyProject compiles and runs fine if I ommit the line

int x = myObject_->TestFunction();

I also have a separate c++ project that tests MyLinkedLibrary.dll by calling the same function and it works fine.
I’ve also double cheked that …MyProject.dll and MyLinkedLibrary.dll are compiled for x64.
Any ideas?

For posterity I will write the solution that I found.
At some point the build process had copied an old version of the dlls into
“C:\Program Files\Epic Games\UE_4.15\Engine\Binaries\Win64” .
I deleted these, recompiled, and it worked.