title: MVVM Foundation: Assertion Failed Error: Invalid Property Name
body: <p>i am just getting started with MVVM Foundation. I am getting </p>
  
  <p><img src="https://i.stack.imgur.com/gbn4u.jpg" alt="alt text"></p>
  
  <p>my codes below: </p>
  
  <p><strong>StartViewModel</strong></p>
  
  <pre><code>class StartViewModel : ObservableObject
  {
      public StartViewModel() {
          _counter = 0;
      }
  
      public ICommand IncrementCommand
      {
          get { return _incrementCommand ?? (_incrementCommand = new RelayCommand(() =&gt; ++Counter)); }
      }
  
      protected int Counter { 
          get { return _counter; } 
          set {
              _counter = value;
              base.RaisePropertyChanged("Counter");
          }
      }
  
      protected int _counter;
      protected RelayCommand _incrementCommand;
  }
  </code></pre>
  
  <p><strong>StartView</strong></p>
  
  <pre><code>&lt;Grid&gt;
      &lt;Grid.RowDefinitions&gt;
          &lt;RowDefinition Height="50*" /&gt;
          &lt;RowDefinition Height="250*" /&gt;
      &lt;/Grid.RowDefinitions&gt;
      &lt;Button Content="Increment" Grid.Row="0" Command="{Binding IncrementCommand}" /&gt;
      &lt;TextBlock Padding="5" Text="{Binding Counter}" Grid.Row="1" /&gt;
  &lt;/Grid&gt;
  </code></pre>
  
  <p>whats wrong with the code? the error appears when i try click the Increment button</p>