@EldHasp thanks for your help. problem with Main_win page solved.
but i have another page with this problem
Win_Login.xaml.cs :
 public partial class Win_login : RibbonWindow 
{
    public Win_login(object @object)
    {
        InitializeComponent();
    }
    public Win_login()
    {
    }
      
    private void btn_login_Click(object sender, RoutedEventArgs e)
    {
      
        if (txt_username.Text == "a" && txt_password.Password == "123")
        {
            Main_win Mainwindow = new Main_win();
            
        }
        else
        {
            MessageBox.Show("user not found");
        }
    }
    private void btn_Exit_Click(object sender, RoutedEventArgs e)
    {
        this.Close();
    }
}
}
win_login.xaml :
<RibbonWindow  x:Class="salesandwarehousingsystem.Win_login"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:salesandwarehousingsystem"
    mc:Ignorable="d"
    Title="Win_login" Height="400" Width="600" Background="Transparent" AllowsTransparency="True" WindowStyle="None" WindowStartupLocation="CenterScreen" >
<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition/>
    </Grid.ColumnDefinitions>
    <Rectangle Stroke="Black" Margin="20,10,0,10" RadiusX=" 15" RadiusY=" 15">
        <Rectangle.Fill>
            <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                <GradientStop Color="#FF134116"/>
                <GradientStop Color="#FF68E370" Offset="1"/>
            </LinearGradientBrush>
        </Rectangle.Fill>
    </Rectangle>
    <Rectangle Stroke="Black" Margin="20,10,0,290" RadiusX=" 15" RadiusY=" 15">
        <Rectangle.Effect>
            <DropShadowEffect/>
        </Rectangle.Effect>
        <Rectangle.Fill>
            <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                <GradientStop Color="#FF0F510E" Offset="1"/>
                <GradientStop Color="#FF1FAE1E" Offset="0"/>
            </LinearGradientBrush>
        </Rectangle.Fill>
    </Rectangle>
    <Label Content="test" HorizontalAlignment="Center" Height="41" Margin="0,19,0,0" VerticalAlignment="Top" Width="491" FontFamily="Segoe Script" FontSize="28" Foreground="#FF0C1462"/>
    <Label Content="Login Form" HorizontalAlignment="Left" Margin="54,65,0,0" VerticalAlignment="Top" Height="45" Width="156" FontSize="24" FontFamily="Segoe Script" Foreground="#FF0C1462"/>
    <Label Content="USER NAME:" HorizontalAlignment="Left" Margin="30,150,0,0" VerticalAlignment="Top" Height="34" Width="91" FontFamily="Arial Black"/>
    <Label Content="PASSWORD :" HorizontalAlignment="Left" Margin="30,200,0,0" VerticalAlignment="Top" Height="39" Width="91" FontFamily="Arial Black"/>
    <TextBox x:Name="txt_username" HorizontalAlignment="Left" Margin="150,154,0,0" TextWrapping="Wrap" Text="" VerticalAlignment="Top" Width="120" Height="26" FontFamily="Arial Narrow" Foreground="White">
        <TextBox.Background>
            <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                <GradientStop Color="Black" Offset="0"/>
                <GradientStop Color="#FFB3B0E8" Offset="1"/>
            </LinearGradientBrush>
        </TextBox.Background>
    </TextBox>
    <Button x:Name="btn_login" Content="LOGIN" HorizontalAlignment="Left" Margin="30,299,0,0" VerticalAlignment="Top" Height="37" Width="91" Foreground="White" Click="btn_login_Click" >
        <Button.Background>
            <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                <GradientStop Color="#FF8F614F" Offset="0.993"/>
                <GradientStop Color="#FF3F1010"/>
                <GradientStop Color="#FF614542" Offset="0.347"/>
            </LinearGradientBrush>
        </Button.Background>
    </Button>
    <Button x:Name="btn_Exit" Content="EXIT" HorizontalAlignment="Left" Margin="150,299,0,0" VerticalAlignment="Top" Height="37" Width="91" Foreground="White" Click="btn_Exit_Click">
        <Button.Background>
            <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                <GradientStop Color="#FF8F614F" Offset="0.993"/>
                <GradientStop Color="#FF3F1010"/>
                <GradientStop Color="#FF614542" Offset="0.347"/>
            </LinearGradientBrush>
        </Button.Background>
    </Button>
    <PasswordBox x:Name="txt_password" HorizontalAlignment="Left" Margin="150,200,0,0" VerticalAlignment="Top" Width="120" Height="29" FontFamily="Arial Narrow" Foreground="White">
        <PasswordBox.Background>
            <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                <GradientStop Color="Black" Offset="0"/>
                <GradientStop Color="#FFB3B0E8" Offset="1"/>
            </LinearGradientBrush>
        </PasswordBox.Background>
    </PasswordBox>
</Grid>
and now this page don't have any binding issues...