Odd exception when combining .hbm.xml and Fluent NHibernate - any ideas?

So, I convert my mapping files as needed (when creating a change, convert to mapping). Anyone when setting up NHibernate like this:

Assembly asm = Assembly.Load("RPMWare.Core.DataAccess");

//NHibernate configuration: see hibernate.cfg.xml
var cfg = new Configuration();
cfg.AddMappingsFromAssembly(asm);
cfg.Configure();

      

        
        
        
      

    

And after running my web application, I get the following exception:

Could not load file or assembly 'NHibernate, Version=2.0.0.4000,
Culture=neutral, PublicKeyToken=aa95f207798dfdb4' or one of its
dependencies. The located assembly manifest definition does not
match the assembly reference. (Exception from HRESULT: 0x80131040)

      

        
        
        
      

    

However, all of my integration tests are working as expected. Any ideas?