Lately i install kwin to my Mate and XFCE but i find out that alt+f2 dont work so use MrGoogr and found that work around.

 
    #include 
    #include 
    #include <X11/Xlib.h>
    void die(const char *message)
    {
       fputs(message, stderr);
       exit(1);
    }
    Atom get_atom(Display *display, const char *atom_name)
    {
       Atom atom = XInternAtom(display, atom_name, False);
       if (atom == None)
          die("can't find an atom I need");
       return atom;
    }
    int main()
    {
       Display *display;
       Atom gnome_panel_atom, run_atom;
       XClientMessageEvent event;
       display = XOpenDisplay(NULL);
       if (display == NULL)
          die("can't open display");
       gnome_panel_atom = get_atom(display, "_MATE_PANEL_ACTION");
       run_atom = get_atom(display, "_MATE_PANEL_ACTION_RUN_DIALOG");
       event.type = ClientMessage;
       event.window = DefaultRootWindow(display);
       event.message_type = gnome_panel_atom;
       event.format = 32;
       event.data.l[0] = run_atom;
       event.data.l[1] = (Time)(time(NULL) * 1000);
       XSendEvent(display, event.window, False, StructureNotifyMask,
                  (XEvent *)&event);
       XCloseDisplay(display);
       return 0;
    }

Copy the code and save as "mate-run.c"
Then compile with "gcc mate-run.c -o mate-run -L/usr/X11R6/lib -lX11"
Make it executable "chmod 755 mate-run"

Then add an keyboard shortcut for Alt+f2 and you solved the issue

May the Kernel be withyou ,Manos

Source:
Mate forums http://forums.mate-desktop.org/viewtopic.php?f=2&t=123
darkness:http://darkness.codefu.org/wordpress/2004/07/popping-up-the-gnome-run-application-dialog-from-a-script/