<p>I am trying to develop a .NET Web Project using NHibernate and Spring.NET, but I'm stuck. Spring.NET seems to depend on different versions of the NHibernate assemblies (maybe it needs 1.2.1.4000 and my NHibernate version is 1.2.0.4000).</p>
<p>I had originally solved similar problems using the &quot;bindingRedirect&quot; tag, but now even that stopped working.</p>
<p><strong>Is there any simple solution to resolve these inter-library relations?</strong></p>

I too ran into this, frustrated I just grabbed the Spring source and compiled it against the latest NHibernate to make it go away forever.  Not sure if that's an option for you but the 10 minutes that took seems to have saved me a lot of time overall.
Here's the SourceForge link for the Spring Source for all versions:
Spring Source