1. Urho3D::URHO3D_API has initializer but incomplete type

This error occurs mostly when trying to migrate from old Urho version (1.32 and older) to newer version. To solve this you have to include Urho3D.h in the problematic files.

#include <Urho3D/Urho3D.h>

This errors did not occur in the older releases because Urho was including Urho3D.h automatically.