WPF Project with View Model in a different project error message: The view does not exist in the current namespage

Question

I have a WPF project (NET6) with a MainWindow and a some views referenced in the MainWindow. The views are in the MainProject with the MainWindow. I have moved my ViewModels in a different project in a class library NET6.

And now the views referenced in the MainWindow are not working, it says: The view does not exist in the current namespace.

There are absolutely no errors, the namespaces are correct as if I move the ModelViews back into the project it solves the View namespace problem

Any idea what the problem can be and how to solve it?

This is the Main Window:

<Window x:Class="CRMT.MainWindow"
        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:CRMT"
        xmlns:view="clr-namespace:CRMT.View"
        xmlns:viewModel = "clr-namespace:CRMT.ViewModels.ViewModel;assembly=CRMT.ViewModels"
        mc:Ignorable="d"
        Title="RCMT" Height="262" Width="500"
        Icon="voice.ico">

    <Window.Resources>
        <DataTemplate DataType="{x:Type viewModel:StartViewModel}">
            <view:StartView />
        </DataTemplate>
        <DataTemplate DataType="{x:Type viewModel:StopViewModel}">
            <view:StopView />
        </DataTemplate>
        <DataTemplate DataType="{x:Type viewModel:EndViewModel}">
            <view:EndView />
        </DataTemplate>
    </Window.Resources>

    <Grid>
        <ContentControl Grid.Row="1" Content="{Binding SelectedViewModel}" />
    </Grid>
</Window>

This is one of the view:

<UserControl x:Class="CRMT.View.StopView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:CRMT.View"
             mc:Ignorable="d" 
             d:DesignHeight="450" d:DesignWidth="800">
    <Grid Background="Green" >
        <Button Margin="10" Width="75" Command="{Binding AddCommand}">
            <StackPanel Orientation="Horizontal">
                <Image Source="/Resources/Images/add.png" Height="18" Margin="0 0 5 0"/>
                <TextBlock Text="Add"/>
            </StackPanel>
        </Button>
    </Grid>
</UserControl>

This is the one of the view xaml.cs

using System.Windows.Controls;

namespace CRMT.View
{
    public partial class StopView : UserControl
    {
        public StopView()
        {
            InitializeComponent();
        }
    }
}

This is the View Model for the StopView:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using CRMT.ViewModels.Command;

namespace CRMT.ViewModels.ViewModel
{
    public class StopViewModel : ViewModelBase
    {

        public DelegateCommand StopCommand { get; }
        public StopViewModel() {
            StopCommand = new DelegateCommand(Stop);
        }

        private void Stop(object? parameter)
        {

        }
    }
}