refering different version of the same GAC assembly

Question

I get this error message while compiling:

Assembly 'MyFramework [...]' uses 'System.Web.Extensions, Version=3.5.0.0 [...]' which has a higher version than referenced assembly 'System.Web.Extensions, Version=1.0.61025.0 [...]'

MyProject refers both System.Web.Extensions 1.0 AND project 'MyFramework', the latter in turn refers web extension 3.5. Both references are Copy local = false, Specific version = true.

The error occurs in MyProject (not in MyFramework). What is wrong here?

I understand that two versions of the same assembly cannot coexsist on the same location, this is why copy local is false.

(I know the setup is lame, it's a huge legacy application, can't just refactor anything.)

UPDATE: there must be something with my project. I created a sample project (for 2.0, referring web extensions 1.0) that uses another sample project(fwk 3.5, web extensions 3.5) an compiles all right. (The way I expected.) So I basically modelled the situation and could not reproduce the problem. The question has changed to:

What may cause the above behaviour? Technically, is there anything wrong in refering two versions of the same strong-named assembly?

UPDATE 2: see accepted answer comments for the root cause. ("Exposed types.") Still need to find the way to solve it.

Answer 1

You have to use extern alias to reference two distinct versions of the same assembly.

Answer 2

You need to add a <bindingRedirect> in App.config.