When using Oracle I am getting this error:
System.Data.OracleClient requires Oracle client software version 8.1.7 or greater.

I was able to successfully integrate NHibernate with MS SQL Server as PostgreSQL but am having all sorts of trouble with Oracle.
Here is an exerpt from my configuration file:

There seems to be a problem here:
<add key="hibernate.dialect" value="NHibernate.Dialect.OracleDialect" />
<add key="hibernate.connection.driver_class" value="NHibernate.Driver.OracleClientDriver" />
<add key="hibernate.connection.connection_string" value="Data Source=glen;User ID=glen;Password=glen;" />

Here is my working MS SQL configuration:
<add key="hibernate.dialect" value="NHibernate.Dialect.MsSql2000Dialect" />
<add key="hibernate.connection.driver_class" value="NHibernate.Driver.SqlClientDriver" />
<add key="hibernate.connection.connection_string" value="server=test;database=nhibernate;uid=nhibernate;pwd=nhibernate;" />

Any ideas or suggestions are greatly appreciated.

-Alan

Does database connectivity with Oracle work using standard ADO.NET? This error is coming from ADO.NET, not NHibernate.

There are a couple of causes for this error. The obvious one is that you need Oracle Client 8.1.7 or greater installed. If you're using the Oracle-provided libraries, I believe you need the 9 client or later installed.

Furthermore, the Oracle Universal[ly hated] Installer messes up the permissions on the directory. You must make sure that the ASPNET user (or whatever user your process will be running under) has Read,List,Execute on the ORACLE_HOME, ORACLE_HOME/Network/Admin, and ORACLE_HOME/bin folders.