Comment 2 for bug 58428

In gnome-panel-2.15.92/applets/clock/clock.c:

static void
calendar_day_activated (ClockData *cd,
                        GtkCalendar *calendar)
{
        unsigned int day;
        unsigned int month;
        unsigned int year;
        char *command_line;
        GError *error;
        gtk_calendar_get_date (GTK_CALENDAR (cd->calendar),
                               &year, &month, &day);
        command_line = g_strdup_printf ("evolution "
                                        "calendar:///?startdate=%.4d%.2d%.2d",
                                        year, month + 1, day);
        //============================================
        error = NULL; // <--- ADD THIS LINE TO SOLVE THIS BUG!!!
        //============================================
        if (!gdk_spawn_command_line_on_screen (gtk_widget_get_screen (cd->calendar),
                                               command_line, &error)) {
                g_printerr ("Cannot launch calendar: %s\n", error->message);
                g_error_free (error);
        }
        g_free (command_line);
}