I'm getting:

Severity	Code	Description	Project	File	Line
Error		Error 42: Symbol Undefined _D3gtk4Main12__ModuleInfoZ		C:\MyProjects\___LIGHTSHOWAPP\WindowsApp1\	
Error		Error 42: Symbol Undefined _D3gtk5Label5Label7__ClassZ		C:\MyProjects\___LIGHTSHOWAPP\WindowsApp1\	
Error		Error 42: Symbol Undefined _D3gtk4Main4Main4initFKAAyaZv (void gtk.Main.Main.init(ref immutable(char)[][]))		C:\MyProjects\___LIGHTSHOWAPP\WindowsApp1\	
Error		Error 42: Symbol Undefined _D3gtk5Label5Label6__ctorMFAyabZC3gtk5Label5Label (gtk.Label.Label gtk.Label.Label.__ctor(immutable(char)[], bool))		C:\MyProjects\___LIGHTSHOWAPP\WindowsApp1\	
Error		Error 42: Symbol Undefined _D3gtk10MainWindow10MainWindow7__ClassZ		C:\MyProjects\___LIGHTSHOWAPP\WindowsApp1\	
Error		Error 42: Symbol Undefined _D3gtk10MainWindow10MainWindow6__ctorMFAyaZC3gtk10MainWindow10MainWindow (gtk.MainWindow.MainWindow gtk.MainWindow.MainWindow.__ctor(immutable(char)[]))		C:\MyProjects\___LIGHTSHOWAPP\WindowsApp1\	
Error		Error 42: Symbol Undefined _D3gtk4Main4Main3runFZv (void gtk.Main.Main.run())		C:\MyProjects\___LIGHTSHOWAPP\WindowsApp1\	
Error		Error 42: Symbol Undefined _D3gtk5Label12__ModuleInfoZ		C:\MyProjects\___LIGHTSHOWAPP\WindowsApp1\	
Error		Error 42: Symbol Undefined _D3gtk10MainWindow12__ModuleInfoZ		C:\MyProjects\___LIGHTSHOWAPP\WindowsApp1\	

For:

import gtk.MainWindow;
import gtk.Label;
import gtk.Main;

void main(string[] args)
{
    Main.init(args);
    MainWindow win = new MainWindow("Hello World");
    win.setDefaultSize(200, 100);
    win.add(new Label("Hello World"));
    win.showAll();
    Main.run();
}

After setting Project Properties > Linker > General > Library Files: gtkd

On Tuesday, 26 January 2016 at 22:04:55 UTC, Enjoys Math wrote:
> [...]

Okay, fixed by changing 'gtkd' setting to 'gtkd.lib'.

On Tuesday, 26 January 2016 at 22:08:23 UTC, Enjoys Math wrote:
> On Tuesday, 26 January 2016 at 22:04:55 UTC, Enjoys Math wrote:
>> [...]
>
> Okay, fixed by changing 'gtkd' setting to 'gtkd.lib'.

I have the same problem. Could you please post the rest of your settings?

Thanks!