[Mono-list] Error compiling GTK# Program

[Paul Paximadis]

When I try and compile the following program( attached ). I get the following error   C:\mono-0.23>mcs -r gtk-sharp basic_form.cs basic_form.cs(36) error CS0246: Cannot find type `Size' Compilation failed: 1 error(s), 0 warnings   Thanks in advance Paul