Using reflection with ASP.NET

[MWells]

I have a simple VS.NET solution with Project "A" as a web app and Project
"B" as a class library.

"B" does some HTML rendering, and uses reflection to locate and load the
necessary rendering classes.

The behavior I'm trying to create is that;

A gives a rendering instruction to B
B uses reflection to locate the specified Renderer
first it looks locally (in B's assembly)
if it cannot locate a match, it looks in A's assembly

The design approach seems simple enough; B (the general library) has some
built-in rendering function but A (a specific app) may need to supply its
own special capabilities.

However I've hit a problem in the implementation; from B,

Assembly.GetExecutingAssembly () returns B's assembly
Assembly.GetCallingAssembly () also returns B's assembly
Assembly.GetEntryAssembly () returns null

This seems inconsistent with the reflection behavior I see in WinForms;
since A originally loaded B, I would have thought at a minimum that A would
be identified as the Entry Assembly, if not the Calling Assembly as well.

Is a different approach required in ASP.NET?

Many thanks for a pointer in the right direction;

/// M