Visual Studio 2010 having problems with x64 assemblies

Question

I have MVC 1.0 project in Visual Studio 2010 on FX 4.0 and fortunately I do not have problems like others do but, well, different ones :)

My project has one mvc project and one class library. When I set both projects to x64 (or AnyCpu) first line of all my aspx pages

<%@ Control Language="VB" Inherits="System.Web.Mvc.ViewUserControl(prj.data.ItemDescriptorModel)" %>

gets blue squiggly line:

Could not load file or assembly 'prj.data' or one of its dependencies. An attempt was made to load a program with an incorrect format.

and whats more important - IntelliSense and syntax coloring stops working in all aspx pages. If I set both projects to x86 then everything works fine. I've checked, class library prj.data depends only on System references, no 3rd party assemblies are referenced.

OS is Windows 7 enterprise x64.