Fluent NHibernate error: Unable to cast object of type ‘Oracle.DataAccess.Client.OracleConnection’ to type ‘System.Data.Common.DbConnection’.

After developing an application in Fluent NHibernate, I’ve received the following Error and Stack Trace:

Unable to cast object of type 'Oracle.DataAccess.Client.OracleConnection' to type 'System.Data.Common.DbConnection'. 
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.InvalidCastException: Unable to cast object of type 'Oracle.DataAccess.Client.OracleConnection' to type 'System.Data.Common.DbConnection'.

Source Error: 

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.  

Stack Trace: 


[InvalidCastException: Unable to cast object of type 'Oracle.DataAccess.Client.OracleConnection' to type 'System.Data.Common.DbConnection'.]
   NHibernate.Tool.hbm2ddl.SuppliedConnectionProviderConnectionHelper.Prepare() +43
   NHibernate.Tool.hbm2ddl.SchemaMetadataUpdater.GetReservedWords(Dialect dialect, IConnectionHelper connectionHelper) +65
   NHibernate.Tool.hbm2ddl.SchemaMetadataUpdater.Update(ISessionFactory sessionFactory) +80
   NHibernate.Impl.SessionFactoryImpl..ctor(Configuration cfg, IMapping mapping, Settings settings, EventListeners listeners) +598
   NHibernate.Cfg.Configuration.BuildSessionFactory() +87
   FluentNHibernate.Cfg.FluentConfiguration.BuildSessionFactory() +49

[FluentConfigurationException: An invalid or incomplete configuration was used while creating a SessionFactory. Check PotentialReasons collection, and InnerException for more detail.

]
   FluentNHibernate.Cfg.FluentConfiguration.BuildSessionFactory() +69
   ETeacherWeb.DataAccess.DataSession.get_SessionFactory() +641
   ETeacherWeb.HttpModules.NHibernateSessionModule.<Init>b__0(Object , EventArgs ) +8
   System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +68
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +75

The server is running Oracle 9.2 client, without ODP.NET. In order to fix this, I copied version 9.2 libraries to the server.

The libraries required were:
Oracle.DataAccess.dll (application/bin folder)
OraOps9.dll (oracle/9.2/bin)

The above directories will of course be different for you, but they should help. Also, the Oracle bin folder must be accessible via the %PATH% variable.

If possible, the much easier fix is to install a full Oracle client, including ODP.NET.

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