validate combo on button click in wpf mvvm

Question

I am creating user control , in which I have placed combo, binded with Enumerations. Binding this enum list has no error.

I try to validate selectedvalue of this combo in button click. But this throw's error while page loads as ,
Value " could not be converted.

If I select 1st option (none) from the list , this error message disapears.
I think, selectedvalue property takes empty string in some where, I can't traceout this.

My coding is as below

<ComboBox x:Name="cbLivingRoomFloorType" Grid.Row="3" Grid.Column="2" BorderBrush="#B6B6B4" BorderThickness="2" ItemsSource="{Binding Path=LivingRoomFloorTypeList}" SelectedValuePath="Value" DisplayMemberPath="Description" SelectedValue="{Binding SelectedLivingRoomType,ValidatesOnDataErrors=True,UpdateSourceTrigger=PropertyChanged}" Margin="0,2"/>

<ContentPresenter x:Name="cpLivingRoom" Grid.Row="4" Grid.Column="2" Content="{Binding Path=(Validation.Errors)[0],ElementName=cbLivingRoomFloorType}">

<ContentPresenter.ContentTemplate>

<DataTemplate>

<TextBlock Foreground="Red" Text="{Binding Path=ErrorContent}" />

</DataTemplate>

</ContentPresenter.ContentTemplate>

</ContentPresenter>

 

In viewmodel

#region Living room

public IEnumerable<ValueDescription> LivingRoomFloorTypeList

{

get

{

return Utility.GetAllValuesAndDescriptions<EnumAptitudeOfLivingRoomFloor>();

}

}

private EnumAptitudeOfLivingRoomFloor _livingRoomFloorType;

public EnumAptitudeOfLivingRoomFloor SelectedLivingRoomType

{

get

{

return _livingRoomFloorType;

}

set

{

if (_livingRoomFloorType == value)

return;

_livingRoomFloorType = value;

RaisePropertyChanged("SelectedLivingRoomType");

}

}

#endregion

I can't trace out the issue. Help me on this.

Thanks in advance