I’ve just updated to the latest version of the Castle stack and got hit with this exception:

The ProxyFactoryFactory was not configured.
Initialize 'proxyfactory.factory_class' property of the session-factory configuration section with one of the available NHibernate.ByteCode providers.
Example:
NHibernate.ByteCode.LinFu.ProxyFactoryFactory, NHibernate.ByteCode.LinFu
Example:
NHibernate.ByteCode.Castle.ProxyFactoryFactory, NHibernate.ByteCode.Castle

Turns out the NHibernate config has changed and as the exception says you must now specify a factory class.

To fix the exception add a new line to your active record facility config:

Nu.Core ** **

Then add a reference in your project to NHibernate.ByteCode.Castle.dll.