Binding visibility.hidden in Xaml

I have a Boolean to Visibility converter

Imports System.Globalization    
Public Class ValueConverters
        Implements IValueConverter
    
        Public Function Convert(ByVal value As Object, ByVal targetType As Type, ByVal parameter As Object, ByVal culture As System.Globalization.CultureInfo) As Object
            Return Visibility.Hidden
        End Function
    
        Public Function ConvertBack(ByVal value As Object, ByVal targetType As Type, ByVal parameter As Object, ByVal culture As System.Globalization.CultureInfo) As Object
            Throw New NotImplementedException()
        End Function
    
        Private Function IValueConverter_Convert(value As Object, targetType As Type, parameter As Object, culture As CultureInfo) As Object Implements IValueConverter.Convert
            Throw New NotImplementedException()
        End Function
    
        Private Function IValueConverter_ConvertBack(value As Object, targetType As Type, parameter As Object, culture As CultureInfo) As Object Implements IValueConverter.ConvertBack
            Throw New NotImplementedException()
        End Function
    End Class

I added the resources in my Xaml

    xmlns:local="clr-namespace:AppKD_2017" d:DataContext="{d:DesignInstance Type=local:A_CreationAssemblage}"
    mc:Ignorable="d"
    Title="Données d'entrée grille de perçage" Height="400" Width="700"
    MaxHeight="460" MaxWidth="700"
    ResizeMode="NoResize" WindowStartupLocation="CenterScreen"
    >
<Window.Resources>
    <local:ValueConverters x:Key="BoolToVis" />
    <!--<BooleanToVisibilityConverter x:Key="BoolToVis" />-->
</Window.Resources>

I have this error message

The name "ValueConverters" does not exist in the "clr-namespace:AppKD_2017" namespace

Your converter has a few problems. The two methods implementing the IValueConverter interface both throw a NotImplementedException. Convert, where you have written some code, will never get called through the interface. Furthermore, it always returns Hidden no matter which Boolean value it receives. Consider these changes:

Imports System.Globalization
Public Class ValueConverters
    Implements IValueConverter

    Public Function Convert(ByVal value As Object, ByVal targetType As Type, ByVal parameter As Object, ByVal culture As System.Globalization.CultureInfo) As Object Implements IValueConverter.Convert
        If value.GetType = GetType(Boolean) Then
            Select Case CType(value, Boolean)
                Case True
                    Return Visibility.Visible
                Case False
                    Return Visibility.Hidden
            End Select
        End If
    End Function

    Public Function ConvertBack(ByVal value As Object, ByVal targetType As Type, ByVal parameter As Object, ByVal culture As System.Globalization.CultureInfo) As Object Implements IValueConverter.ConvertBack
        Throw New NotImplementedException()
    End Function

End Class 

Finally, you probably have to Build your project before the converter is recognized by the XAML editor.