Could not load the assembly 'App_Web_xxx'. Make sure that it is compiled before accessing the page.

Recently I was deploying a module of a website on top of another virtual directory.

Of course the simplest way is to make this directory as an IIS application, but that's the last option.

What I did was to override the "base" web.config file and add the following lines:

<configuration>
   <runtime>
      <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
         <probing privatePath="bin;MYDIRECTORY/BIN"/>
      </assemblyBinding>
   </runtime>
</configuration>

What it basically does, is tell the IIS to look for bin objects in the MYDIRECTORY/BIN folder relative to the virtual directory itself.