Error while installing npgsql for .net Application with Ibatis

Below error is populated when the .net application is configured for Npgsql (Postgresql) along with Ibatis.

Could not load file or assembly 'Npgsql\, Version\=v4.0.30319\, Culture\=neutral\, PublicKeyToken\=5d8b90d52f46fda7' or one of its dependencies. The given assembly name or codebase was invalid. (Exception from HRESULT: 0x80131047)"} System.Exception {IBatisNet.Common.Exceptions.ConfigurationException}

• runtime ibatis version v2.0.50727

• npgsql version runtime v4.0.30319

• npgsql version 4.1.3.1

• net version 4.1

• Visual Studio 2015