Adding assembly reference within web.config

Are all of projA's dependencies in projB? Usually I'd just add a reference from one project to another if they are in the same solution.

Edit:

If you want to add an assembly dynamically then maybe a service reference maybe something to consider. By dumping in projA's DLL into the bin that doesn't really give all the DLLs that it may require, thus there are ways to tie things together so that objects can be understood across systems, like web services using XML to give a common example.

My question back about adding an assembly dynamically is where would you get it from and can that part be automated to be part of projB as that is really the general solution to this kind of problem.

Edit 2:

How could you get all of projA's dependencies? Is it possible to get it so that it doesn't depend on a bunch of other DLLs that may or may not be on the system that this is to run. That is what the error is telling you, that there exists some assembly projC that is also required. Note that this adding of assemblies can continue for a long time if there are many levels of dependencies used.

Summarizing the answer: What would you need to reference in order to load projA into some new project? That's your problem which without knowing what the dependencies look like is rather hard to answer directly.

It is quite simple. Look at your compilation section in your web.config:

<compilation debug="true" targetFramework="4.0"/>

Now open the section and put your assembly inside like this:

<compilation debug="true" targetFramework="4.0">
  <assemblies>
    <add assembly="System.Data.Entity, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" />
  </assemblies>
</compilation>

Libraries in this section are checked in compilation time, it has nothing to do with runtime binding.