Today Steve Evans a friend of mine hit me up asking what version of Fluent I was using because he was running into issues with the current version of Fluent and NHibernate.  I started to investigate and ran into the same problem.  Basically it was causing an error due to a new dependency that was not with the binary or source versions of Fluent. 

The reason there is issues with NHibernate currently is because there was a change in NHibernate 2.1.  In the past there was a hard coded dependency on Castle’s DynamicProxy2.  This has been changed now to allow freedom of choice.  Currently you can choose LinFu or Castle. 

If you currently download Build (#535) you are going to have to do some massaging.  Here are the steps I did to get Fluent working in my current project with Castle Proxy.

1. Download Fluent Binary from Here.
2. Extract the Zip file to your local disk.  In my case this is c:\Development\Code Dependencies\FluentNHibernate\
3. Download ActiveRecord from Castle Project Site.  Download This.
4. Extract ActiveRecord or Just copy all of the DLLs over the DLLs in your FluentNHibernate Folder. 
5. Add/Change your references in your project to the NHibernate.dll, FluentNHibernate.dll, and NHibernate.ByteCode.Castle.dll

I have also created a zip of just the DLLs which you could also use: Download My Copy of the DLLs.