Commented by: @cincuranet

It's because you're running on Mono, but the build isn't done with MONO directive. And BTW doing blind try-catch to solve problem isn't a good idea.

Commented by: Konstantin Dombrugov (abracadabra)

1) this is not blind try-catch

according to MSDN
Encoding.GetEncoding(string)
exceptions:
ArgumentException
name is not a valid code page name.
-or-
The code page indicated by name is not supported by the underlying platform.

And I need only 3 encodings... not the whole list of supported encodings.

2) Sorry, but need to have TWO diffrent builds of the same assembly is a really bad idea. My software can work on Windows (.net 2.0) or Linux (Mono 2.*) on the same build.
I think, it's better to use runtime check instread of compilation directives.
public static Boolean IsRunningOnLinux()
{
var p = (int)Environment.OSVersion.Platform;
return (p == 4) || (p == 128);
}

    public static Boolean IsRunningOnMono\(\)
    \{
        return Type\.GetType\("Mono\.Runtime"\) \!= null;
    \}

Commented by: @cincuranet

We have to have Mono build, because some parts of code are not working there. The runtime check isn't enough, in some parts we need to know this during compile time. If you need to use it on Mono and on http://MS.NET, use MONO directive. It's compatible with http://MS.NET.