Question

I have a button that is enabled depending on two properties. I used a MultiBinding with a Converter.

Everything works but the output keeps saying:

System.Windows.Data Error: 5 : Value produced by BindingExpression is not valid for target property.; Value='' MultiBindingExpression:target element is 'HGCCommandButton' (Name='btnEliminar'); target property is 'IsEnabled' (type 'Boolean')

There are some questions here with similar issues:
WPF MultiBinding Fails. Why?

Any easy solution or I should make the logic in the ViewModel and bind just to one property?

CODE:
XAML:

<utils:HGCCommandButton x:Name="btnEliminar">
                    <utils:HGCCommandButton.IsEnabled>
                        <MultiBinding Converter="{StaticResource MultiValueIsEnabledConverter}"
                                      ConverterParameter="NotEnabledIfIsFromInfoGestionOrIsNew">
                            <Binding Path="IsNew" />
                            <Binding Path="IsAbonado" />
                        </MultiBinding>
                    </utils:HGCCommandButton.IsEnabled>
                </utils:HGCCommandButton>

Converter:

public class MultiValueIsEnabledConverter : IMultiValueConverter
    {
        public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
        {
            if (parameter!=null)
            {
                if (values[0] == DependencyProperty.UnsetValue || values[1] == DependencyProperty.UnsetValue) return "";

                var sel = (MultiValueIsEnabledConverterNames)Enum.Parse(typeof(MultiValueIsEnabledConverterNames), parameter.ToString());

                switch (sel)
                {
                   ...

                    case MultiValueIsEnabledConverterNames.NotEnabledIfIsFromInfoGestionOrIsNew:
                        return (bool)NotEnabledIfIsFromInfoGestionOrIsNew(values[0], values[1]);

                    default:
                        throw new ArgumentOutOfRangeException();
                }
            }

            return false;
        }
    private static object NotEnabledIfIsFromInfoGestionOrIsNew(object isFromIG, object isNew)
            {
                if ((isFromIG != null) && !(bool)isFromIG)
                {
                    if ((isNew != null) && !(bool)isNew) 
                    {
                        return !((bool)isFromIG && (bool)isNew);
                    }
                    return false;
                }
                return false;
            }

ViewModel variables are just two booleans

Answer 1

That is quite an odd ConverterParameter, is the StaticResource you reference for the Converter actually an instance of the converter whose code you posted? The error claims that the value is not a bool and that method alone can only return a bool so i doubt that the error is found here.

Can the code in your Convert method return anything else but a bool? You need to avoid it if that is possible.

Edit: Right here is the problem:

if (values[0] == DependencyProperty.UnsetValue || values[1] == DependencyProperty.UnsetValue) return "";

You return an empty string which is not compatible with the boolean property,