I am using ubuntu 11.11 and mono,
Under references/gtk-sharp, I am shown
"Assembly not available for Mono/.NET 2.0(in Mono 2.10.5)"
How do I resolve this?
Ubuntu has policy of only including only one version of a package. In ubuntu 11.11 the version of mono that is included supports .net 4. So any program referencing .net 2.0 assemblies will not work. You need to change your project to .net 4.0 and update your references to use the .net 4.0 version of the assemblies you need.
As an example, the following invocation remedied the identical issue you mention for me:
mono --runtime=v4.0 hello.exe
Otherwise the runtime version defaults to v2.0.50727.