VSIX - Cannot load assembly of a referenced dll (VisualStudio 2015)

Question

i have referenced MaterialDesignThemes.Wpf.dll and MaterialDesigncolors.Wpf.dll to the newly created VSIX project in VisualStudio 2015. then i added below code between Grid Tags

 <Grid.Resources>
            <ResourceDictionary>
                <ResourceDictionary.MergedDictionaries>
                    <ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.Light.xaml"></ResourceDictionary>
                    <ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.Defaults.xaml" />
                    <ResourceDictionary Source="pack://application:,,,/MaterialDesignColors;component/Themes/Recommended/Primary/MaterialDesignColor.DeepPurple.xaml" />
                    <ResourceDictionary Source="pack://application:,,,/MaterialDesignColors;component/Themes/Recommended/Accent/MaterialDesignColor.Lime.xaml" />
                </ResourceDictionary.MergedDictionaries>
            </ResourceDictionary>
        </Grid.Resources>

it builds successfully, but when run i get an exception saying,

Set property 'System.Windows.ResourceDictionary.Source' threw an exception. Inner Exception Could not load file or assembly 'MaterialDesignThemes.Wpf

even i cannot add my own classlibrary (class1.dll)

your assistance in this matter is greatly appreciated