NHibernate 1.2 in a .NET 4.0 solution

Question

I have some projects based on NHibernate 1.2 and I'd like to add them to a .NET 4.0 solution, but I get an AmbiguousMatchException.
No matter if these projects are targeted to 2.0 or 4.0 framework.
It works if I add them to a .NET 3.5 solution.

Does anyone have experience with that?

Here is the exception:

[AmbiguousMatchException: Ambiguous match found.]
   System.RuntimeType.GetMethodImpl(String name, BindingFlags bindingAttr, Binder binder, CallingConventions callConv, Type[] types, ParameterModifier[] modifiers) +9607924
   System.Type.GetMethod(String name) +29
   Castle.DynamicProxy.Builder.CodeBuilder.SimpleAST.LockBlockExpression.Emit(IEasyMember member, ILGenerator gen) +192
   Castle.DynamicProxy.Builder.CodeBuilder.SimpleAST.ExpressionStatement.Emit(IEasyMember member, ILGenerator gen) +52
   Castle.DynamicProxy.Builder.CodeBuilder.AbstractCodeBuilder.Generate(IEasyMember member, ILGenerator il) +370
   Castle.DynamicProxy.Builder.CodeBuilder.EasyMethod.Generate() +71
   Castle.DynamicProxy.Builder.CodeBuilder.AbstractEasyType.EnsureBuildersAreInAValidState() +706
   Castle.DynamicProxy.Builder.CodeBuilder.AbstractEasyType.BuildType() +90
   Castle.DynamicProxy.Builder.CodeGenerators.BaseCodeGenerator.CreateType() +55
   Castle.DynamicProxy.Builder.CodeGenerators.ClassProxyGenerator.GenerateCode(Type baseClass, Type[] interfaces) +573
   Castle.DynamicProxy.Builder.DefaultProxyBuilder.CreateClassProxy(Type theClass, Type[] interfaces) +87
   Castle.DynamicProxy.ProxyGenerator.CreateClassProxy(Type baseClass, Type[] interfaces, IInterceptor interceptor, Boolean checkAbstract, Object[] argumentsForConstructor) +116
   NHibernate.Proxy.CastleProxyFactory.GetProxy(Object id, ISessionImplementor session) +136

[HibernateException: Creating a proxy instance failed]
   NHibernate.Proxy.CastleProxyFactory.GetProxy(Object id, ISessionImplementor session) +270
   NHibernate.Persister.Entity.AbstractEntityPersister.CreateProxy(Object id, ISessionImplementor session) +17
   NHibernate.Impl.SessionImpl.DoLoadByClass(Type clazz, Object id, Boolean checkDeleted, Boolean allowProxyCreation) +354
   NHibernate.Impl.SessionImpl.InternalLoad(Type clazz, Object id, Boolean eager, Boolean isNullable) +52
   NHibernate.Type.EntityType.ResolveIdentifier(Object id, ISessionImplementor session) +37
   NHibernate.Type.EntityType.ResolveIdentifier(Object id, ISessionImplementor session, Object owner) +55
   NHibernate.Impl.SessionImpl.InitializeEntity(Object obj) +187
   NHibernate.Loader.Loader.InitializeEntitiesAndCollections(IList hydratedObjects, Object resultSetId, ISessionImplementor session) +229
   NHibernate.Loader.Loader.DoQuery(ISessionImplementor session, QueryParameters queryParameters, Boolean returnProxies) +702
   NHibernate.Loader.Loader.DoQueryAndInitializeNonLazyCollections(ISessionImplementor session, QueryParameters queryParameters, Boolean returnProxies) +62
   NHibernate.Loader.Loader.DoList(ISessionImplementor session, QueryParameters queryParameters) +51
   NHibernate.Loader.Loader.ListIgnoreQueryCache(ISessionImplementor session, QueryParameters queryParameters) +18
   NHibernate.Loader.Loader.List(ISessionImplementor session, QueryParameters queryParameters, ISet querySpaces, IType[] resultTypes) +81
   NHibernate.Loader.Criteria.CriteriaLoader.List(ISessionImplementor session) +36
   NHibernate.Impl.SessionImpl.Find(CriteriaImpl criteria, IList results) +315
   NHibernate.Impl.SessionImpl.Find(CriteriaImpl criteria) +66
   NHibernate.Impl.CriteriaImpl.List() +54  
   [my code calling Criteria.List()]

Answer 1

Following Rup's comment, I resolved changing the sources of Castle DynamicProxy 1.1.5 and recompiling.
The problem is invoking with reflection the method System.Threading.Monitor.Enter without specifying arguments (that's because in .NET 2.0 there is only 1 signature), but since .NET 4.0 that method has 2 overloads.

I've modified the class Castle.DynamicProxy.Builder.CodeBuilder.SimpleAST.LockBlockExpression, changing the row

gen.Emit(OpCodes.Call, typeof(Monitor).GetMethod("Enter"));

with the row

gen.Emit(OpCodes.Call, typeof(Monitor).GetMethod("Enter", new Type[] { typeof(object) }));

I've got the sources of NHibernate 1.2 from SourceForge while I disassembled the code of Castle DynamicProxy 1.1.5 with Reflector.