C# mode on Linux: flymake inactive

[torys.anderson@gmail.com]

I am trying to develop C# applications on Linux and have installed CSharp-mode and Flymake as per all the direction here: http://www.emacswiki.org/emacs/CSharpMode

I have the following code in my .emacs for initialization:

        (autoload 'csharp-mode "csharp-mode" "Major mode for editing C# code." t)
        (setq auto-mode-alist  (append '(("\\.cs$" . csharp-mode)) auto-mode-alist))

        ;; Custom code to use a default compiler string for all C# files
        (defvar my-csharp-default-compiler nil)
        (setq my-csharp-default-compiler "gmcs @@FILE@@")

        (defun my-csharp-get-value-from-comments (marker-string line-limit)
          my-csharp-default-compiler)

        (add-hook 'csharp-mode-hook (lambda ()
                                      (if my-csharp-default-compiler
                                          (progn
                                            (fset 'orig-csharp-get-value-from-comments
                                                  (symbol-function 'csharp-get-value-from-comments))
                                            (fset 'csharp-get-value-from-comments
                                                  (symbol-function 'my-csharp-get-value-from-comments))))
                                      (flymake-mode)))
        (add-hook 'csharp-mode-hook
                  (lambda ()
                    (local-set-key (kbd "{") 'c-electric-brace)))

If I make a little demo program I am able to simply compile and run it with `gmcs myfile.cs` and `mono myfile.exe`. However, Flymake mode does absolutely nothing; no errors, no popups, no syntax checking. Although my mode-line indicates Flymake is running (with no exception marks), absolutely nothing happens. Any suggestions on how to get it working?