Plugins: Unable to load type xxx.xxx.PluginFactory from the plugin assembly

Hello,

I'm upgrading my server application to 4.0 server's plugin system, and getting this error starting the server:

...
2016-06-29 10:48:54,181 [1] ERROR Photon.Hive.Plugin.PluginManager - Got Exception during either loading of assembly C:\PhotonServer4\deploy\Plugins\BigBogglerPlugin\\bin\PhotonHive.BigBogglerPlugin.dll or type Xidea.BigBoggler.BigBogglerPlugin.PluginFactory.
Exception System.TypeLoadException: Impossibile caricare il tipo 'Xidea.BigBoggler.BigBogglerPlugin.PluginFactory' dall'assembly 'PhotonHive.BigBogglerPlugin, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.
   in System.Reflection.RuntimeAssembly.GetType(RuntimeAssembly assembly, String name, Boolean throwOnError, Boolean ignoreCase, ObjectHandleOnStack type)
   in System.Reflection.RuntimeAssembly.GetType(String name, Boolean throwOnError, Boolean ignoreCase)
   in Photon.Hive.Plugin.PluginManager.CreateKnownType(String typeName, Assembly asm) in d:\dev\photon-socketserver-sdk_cloud\src-server\Hive\PhotonHive\Plugin\PluginManager.cs:riga 429
   in Photon.Hive.Plugin.PluginManager.SetupPluginManager(String path, String typeName, Dictionary`2 config) in d:\dev\photon-socketserver-sdk_cloud\src-server\Hive\PhotonHive\Plugin\PluginManager.cs:riga 338

The implementation is in VB.NET and figure as follows:

Namespace Xidea.BigBoggler.BigBogglerPlugin
    Public Class PluginFactory
        Implements IPluginFactory
        Public Function Create(gameHost As IPluginHost, pluginName As String, config As Dictionary(Of String, String), ByRef errorMsg As String) As IGamePlugin Implements IPluginFactory.Create
            Dim plugin = New BigBogglerPlugin

            If plugin.SetupInstance(gameHost, config, errorMsg) Then
                Return plugin
            End If
            Return Nothing
        End Function
    End Class
End Namespace

The config section is:

  <PluginSettings Enabled="true">
    <Plugins>
      <Plugin
              Name="BigBogglerPlugin"
              Version=""
              AssemblyName="PhotonHive.BigBogglerPlugin.dll"
              Type="Xidea.BigBoggler.BigBogglerPlugin.PluginFactory"
              BaseUrl="http://photon-photon-pluginsdk-v1.webscript.io"
              IsPersistent="true"
              HasErrorInfo="true"
              PathClose="GameClose"
              PathCreate="GameCreate"
              PathEvent="GameEvent"
              PathGameProperties="GameProperties"
              PathJoin="GameJoin"
              PathLeave="GameLeave"
              PathLoad="GameCreate" />
    </Plugins>
  </PluginSettings>

What do I missing? Is this issue related to VB coding?

thanks in advance,

Flavio