Hi Michael with valac 0.11.5-0ubuntu1, I got this error in natty with git master branch.

# make
valac -C --pkg gtk+-2.0 --pkg gdk-2.0 --pkg Config --pkg posix --pkg gconf-2.0 --vapidir src/ --basedir . src/MainWindow.vala src/Main.vala src/SettingsDialog.vala src/Settings.vala src/SendProgressDialog.vala src/ReceiveChooserDialog.vala src/ReceiveProgressDialog.vala src/RecordDialog.vala src/PreferencesDialog.vala src/SerialConnection.vala src/HexTextBuffer.vala src/SerialStreamRecorder.vala src/InputParser.vala src/Rzwrapper.vala src/XmodemFilenameDialog.vala src/SendChooserDialog.vala src/Szwrapper.vala src/AutoScroll.vala src/Preferences.vala src/Profile.vala src/DefaultPaths.vala src/MoUtils.vala
src/Profile.vala:103.14-103.17: error: Argument 1: Cannot convert from `string?' to `uint8[]'
			fos.write(data, s, null);
			          ^^^^
src/InputParser.vala:31.2-31.31: error: error type `HexParseError` is less accessible than method `InputParser.parseHex`
	public static uchar[] parseHex(string s) throws HexParseError {
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
src/SendChooserDialog.vala:35.36-35.51: warning: Gtk.STOCK_CANCEL has been deprecated since vala-0.12. Use Gtk.Stock.CANCEL
                dialog.add_buttons(Gtk.STOCK_CANCEL, Gtk.ResponseType.CANCEL, Gtk.STOCK_OK, Gtk.ResponseType.ACCEPT, null);
                                   ^^^^^^^^^^^^^^^^
src/SendChooserDialog.vala:35.79-35.90: warning: Gtk.STOCK_OK has been deprecated since vala-0.12. Use Gtk.Stock.OK
                dialog.add_buttons(Gtk.STOCK_CANCEL, Gtk.ResponseType.CANCEL, Gtk.STOCK_OK, Gtk.ResponseType.ACCEPT, null);
                                                                              ^^^^^^^^^^^^
src/ReceiveChooserDialog.vala:36.36-36.51: warning: Gtk.STOCK_CANCEL has been deprecated since vala-0.12. Use Gtk.Stock.CANCEL
                dialog.add_buttons(Gtk.STOCK_CANCEL, Gtk.ResponseType.CANCEL, Gtk.STOCK_OK, Gtk.ResponseType.ACCEPT, null);
                                   ^^^^^^^^^^^^^^^^
src/ReceiveChooserDialog.vala:36.79-36.90: warning: Gtk.STOCK_OK has been deprecated since vala-0.12. Use Gtk.Stock.OK
                dialog.add_buttons(Gtk.STOCK_CANCEL, Gtk.ResponseType.CANCEL, Gtk.STOCK_OK, Gtk.ResponseType.ACCEPT, null);
                                                                              ^^^^^^^^^^^^
src/SerialStreamRecorder.vala:49.18-49.18: error: Argument 2: Cannot convert from `int' to `GLib.Cancellable?'
				fos.write(o, 1, null);
				             ^
src/RecordDialog.vala:40.36-40.51: warning: Gtk.STOCK_CANCEL has been deprecated since vala-0.12. Use Gtk.Stock.CANCEL
                dialog.add_buttons(Gtk.STOCK_CANCEL, Gtk.ResponseType.CANCEL, Gtk.STOCK_SAVE, Gtk.ResponseType.ACCEPT, null);
                                   ^^^^^^^^^^^^^^^^
src/RecordDialog.vala:40.79-40.92: warning: Gtk.STOCK_SAVE has been deprecated since vala-0.12. Use Gtk.Stock.SAVE
                dialog.add_buttons(Gtk.STOCK_CANCEL, Gtk.ResponseType.CANCEL, Gtk.STOCK_SAVE, Gtk.ResponseType.ACCEPT, null);
                                                                              ^^^^^^^^^^^^^^
src/Rzwrapper.vala:172.9-172.20: warning: string.str is deprecated. Use string.index_of
			if(!(messages.str("Transfer complete")==null)) {
			     ^^^^^^^^^^^^
src/Rzwrapper.vala:175.9-175.20: warning: string.str is deprecated. Use string.index_of
			if(!(messages.str("Transfer incomplete")==null)) {
			     ^^^^^^^^^^^^
src/Szwrapper.vala:163.9-163.20: warning: string.str is deprecated. Use string.index_of
			if(!(messages.str("Transfer complete")==null)) {
			     ^^^^^^^^^^^^
src/Szwrapper.vala:167.9-167.20: warning: string.str is deprecated. Use string.index_of
			if(!(messages.str("Transfer incomplete")==null)) {
			     ^^^^^^^^^^^^
src/MainWindow.vala:845.36-845.51: warning: Gtk.STOCK_CANCEL has been deprecated since vala-0.12. Use Gtk.Stock.CANCEL
                dialog.add_buttons(Gtk.STOCK_CANCEL, Gtk.ResponseType.CANCEL, Gtk.STOCK_SAVE, Gtk.ResponseType.ACCEPT, null);
                                   ^^^^^^^^^^^^^^^^
src/MainWindow.vala:845.79-845.92: warning: Gtk.STOCK_SAVE has been deprecated since vala-0.12. Use Gtk.Stock.SAVE
                dialog.add_buttons(Gtk.STOCK_CANCEL, Gtk.ResponseType.CANCEL, Gtk.STOCK_SAVE, Gtk.ResponseType.ACCEPT, null);
                                                                              ^^^^^^^^^^^^^^
src/MainWindow.vala:863.36-863.51: warning: Gtk.STOCK_CANCEL has been deprecated since vala-0.12. Use Gtk.Stock.CANCEL
                dialog.add_buttons(Gtk.STOCK_CANCEL, Gtk.ResponseType.CANCEL, Gtk.STOCK_OPEN, Gtk.ResponseType.ACCEPT, null);
                                   ^^^^^^^^^^^^^^^^
src/MainWindow.vala:863.79-863.92: warning: Gtk.STOCK_OPEN has been deprecated since vala-0.12. Use Gtk.Stock.OPEN
                dialog.add_buttons(Gtk.STOCK_CANCEL, Gtk.ResponseType.CANCEL, Gtk.STOCK_OPEN, Gtk.ResponseType.ACCEPT, null);
                                                                              ^^^^^^^^^^^^^^
Compilation failed: 3 error(s), 14 warning(s)
make: *** [src/moserial.vala.stamp] Error 1