Graphics memG  = Graphics.FromImage(memoryBitmap);

if (!mono)
{
    Bitmap  skin   = SnapForms.Properties.Resources.Skin;
    ^^^^ does not work with mono, but the following does:
}
else
{
    Bitmap  skin    = (Bitmap) Bitmap.FromFile("Skin.jpg");
}

The code does not error out until here:
memG.DrawImage(skin, new Rectangle(Width - 104, 0, 103, 27), new Rectangle(skin.Width - 103, 0, 103, 27), GraphicsUnit.Pixel);

The error is:
Unhandled Exception: System.ArgumentException: Invalid Parameter. A null referen
ce or invalid value was found.
  at System.Drawing.GDIPlus.CheckStatus (Status status) [0x0006d] in C:\cygwin\t
mp\scratch\mono-1.2.3.1\mcs\class\System.Drawing\System.Drawing\gdipFunctions.cs
:200
  at System.Drawing.Image.get_PixelFormat () [0x0000e] in C:\cygwin\tmp\scratch\
mono-1.2.3.1\mcs\class\System.Drawing\System.Drawing\Image.cs:617
  at (wrapper remoting-invoke-with-check) System.Drawing.Image:get_PixelFormat (
)
  at SnapForms.SkinnedForm.GenerateBackground () [0x00000]
  at SnapForms.SkinnedForm.SkinnedForm_Resize (System.Object sender, System.Even
tArgs e) [0x00000]
  at (wrapper delegate-invoke) System.MulticastDelegate:invoke_void_object_Event
Args (object,System.EventArgs)
  at System.Windows.Forms.Control.OnResize (System.EventArgs e) [0x00028] in C:\
cygwin\tmp\scratch\mono-1.2.3.1\mcs\class\Managed.Windows.Forms\System.Windows.F
orms\Control.cs:5291
  at System.Windows.Forms.Form.OnResize (System.EventArgs e) [0x00000] in C:\cyg
win\tmp\scratch\mono-1.2.3.1\mcs\class\Managed.Windows.Forms\System.Windows.Form
s\Form.cs:1782
  at System.Windows.Forms.Control.OnSizeChanged (System.EventArgs e) [0x00006] i
n C:\cygwin\tmp\scratch\mono-1.2.3.1\mcs\class\Managed.Windows.Forms\System.Wind
ows.Forms\Control.cs:5305
  at System.Windows.Forms.Control.UpdateBounds (Int32 x, Int32 y, Int32 width, I
nt32 height, Int32 clientWidth, Int32 clientHeight) [0x000ec] in C:\cygwin\tmp\s
cratch\mono-1.2.3.1\mcs\class\Managed.Windows.Forms\System.Windows.Forms\Control
.cs:4311
  at System.Windows.Forms.Control.UpdateBounds (Int32 x, Int32 y, Int32 width, I
nt32 height) [0x0002e] in C:\cygwin\tmp\scratch\mono-1.2.3.1\mcs\class\Managed.W
indows.Forms\System.Windows.Forms\Control.cs:4274
  at System.Windows.Forms.Control.SetBoundsCore (Int32 x, Int32 y, Int32 width,
Int32 height, BoundsSpecified specified) [0x0004a] in C:\cygwin\tmp\scratch\mono
-1.2.3.1\mcs\class\Managed.Windows.Forms\System.Windows.Forms\Control.cs:4146
  at System.Windows.Forms.Form.SetBoundsCore (Int32 x, Int32 y, Int32 width, Int
32 height, BoundsSpecified specified) [0x00000] in C:\cygwin\tmp\scratch\mono-1.
2.3.1\mcs\class\Managed.Windows.Forms\System.Windows.Forms\Form.cs:1940
  at System.Windows.Forms.Control.SetBounds (Int32 x, Int32 y, Int32 width, Int3
2 height, BoundsSpecified specified) [0x00048] in C:\cygwin\tmp\scratch\mono-1.2
.3.1\mcs\class\Managed.Windows.Forms\System.Windows.Forms\Control.cs:3689
  at System.Windows.Forms.Control.set_Height (Int32 value) [0x00000] in C:\cygwi
n\tmp\scratch\mono-1.2.3.1\mcs\class\Managed.Windows.Forms\System.Windows.Forms\
Control.cs:2521
  at SnapForms.MessageWindow..ctor (SnapForms.SkinnedForm _parent) [0x00000]
  at (wrapper remoting-invoke-with-check) SnapForms.MessageWindow:.ctor (SnapFor
ms.SkinnedForm)
  at SnapForms.Program.Main () [0x00000]