C # 'cannot access properties of anonymous types declared in another assembly

Possible duplicate:
C # 4.0 Dynamics

I have a function

void Foo(dynamic thingy)
{

  int bar = thingy.Id;
}

and i call it that

Foo(new {Id=42, Color="red", size = "XL"});

This works great when Foo and the caller are in the same assembly. But when they are not in the same assembly, Foo crashes at runtime with a RuntimeBinderException, saying

'object' does not contain a definition for 'Id'

pointing to the string thingy.Id. The clock in VS shows that it has the Id property. Any ideas?

EDIT: this will be closed by dup. But I thought I would just record the fact that the internally visible attribute of the assembly worked perfectly - tx manji