ArgumentNullException can be thrown when opening a RadOpenFileDialog in the following scenario: CustomPlaces contains the Desktop directory, InitialDirectory is also set to Desktop and ShowNetworkLocations is false. 

System.Windows.Data Error: 8 : Cannot save value from target back to source. BindingExpression:Path=CurrentParentDirectory; DataItem='OpenFileDialogViewModel' (HashCode=57416810); target element is 'FileDialogsBreadcrumb' (Name='PART_PathNavigationPane'); target property is 'CurrentItem' (type 'Object') ArgumentNullException:'System.ArgumentNullException: Value cannot be null.
Parameter name: value
   at System.String.StartsWith(String value)
   at Telerik.Windows.Controls.FileDialogs.Helpers.PathHelper.CapitalizeNetworkPath(String path)
   at Telerik.Windows.Controls.FileDialogs.ExplorerControl.BringItemIntoView(DirectoryBaseWrapper itemToBring)
   at Telerik.Windows.Controls.FileDialogs.ExplorerControl.SyncTreeViewWithCurrentDir()
   at Telerik.Windows.Controls.FileDialogs.ExplorerControl.ProcessCurrentParentDirChanged()
   at System.ComponentModel.PropertyChangedEventHandler.Invoke(Object sender, PropertyChangedEventArgs e)
   at Telerik.Windows.Controls.ViewModelBase.OnPropertyChanged(String propertyName)
   at Telerik.Windows.Controls.FileDialogs.OpenFileDialogViewModel.OnPropertyChanged(String propertyName)
   at Telerik.Windows.Controls.FileDialogs.DialogViewModel.set_CurrentParentDirectory(DirectoryBaseWrapper value)'