Why can't I compile with UE4 open?

It is currently not possible for me to compile any code changes when UE4 is open (using VS 2013 Express). When I close UE4 I can compile it without problems. This is pretty bad for a iterative workflow.

I hope you can help me

Because your compiled dll is loaded by ditor and can not be edited. But you can use compile button in editor and it will automatically reload the dll, but it only works when your changes does not change structure of classes. I bet overtime reloading gonna be improved.

Been thinking the same. But compiling in UE4 did not work aswell and my changes were minor (changing the value of a variable)

Apiotrw, it all depends on where you changed the value. If you changed the default value in the constructor, then you need to reload editor, if you changed default value in, like: BeginPlay, then you wouldn’t had to reload editor.