Cannot compile Mono.Addins

Cannot compile Mono.Addins

I've tried to compile the current version of Mono.Addins, but it failed
with the following error messages:
Building Mono.Addins.Gui.csproj
/usr/lib/mono/4.0/Microsoft.Common.targets: warning : Reference
'glib-sharp, Version=2.12.0.0, Culture=neutral,
PublicKeyToken=35e10195dab3c99f' not resolved
/usr/lib/mono/4.0/Microsoft.Common.targets: warning : Reference
'pango-sharp, Version=2.12.0.0, Culture=neutral,
PublicKeyToken=35e10195dab3c99f' not resolved
/usr/lib/mono/4.0/Microsoft.Common.targets: warning : Reference
'atk-sharp, Version=2.12.0.0, Culture=neutral,
PublicKeyToken=35e10195dab3c99f' not resolved
/usr/lib/mono/4.0/Microsoft.Common.targets: warning : Reference
'gdk-sharp, Version=2.12.0.0, Culture=neutral,
PublicKeyToken=35e10195dab3c99f' not resolved
/usr/lib/mono/4.0/Microsoft.Common.targets: warning : Reference
'gtk-sharp, Version=2.12.0.0, Culture=neutral,
PublicKeyToken=35e10195dab3c99f' not resolved
Mono.Addins.Gui/AddinManagerDialog.cs(30,7): error CS0246: The type or
namespace name Gtk' could not be found. Are you missing an assembly
reference?
Mono.Addins.Gui/AddinTreeWidget.cs(32,7): error CS0246: The type or
namespace nameGtk' could not be found. Are you missing an assembly
reference?
Mono.Addins.Gui/AddinTreeWidget.cs(33,7): error CS0246: The type or
namespace name Gdk' could not be found. Are you missing an assembly
reference?
Mono.Addins.Gui/ManageSitesDialog.cs(31,7): error CS0246: The type or
namespace nameGtk' could not be found. Are you missing an assembly
reference?
I've alread installed the current versions of Mono and Gtk# from sources.
Any idea what's going wrong?