Error loading custom extension assembly - "The parameter is incorrect"

SSRS2012 fails to load my custom authentication assembly.  I see this error in the logs:

extensionfactory!ReportServer_0-2!10d8!01/02/2015-23:34:49:: e ERROR: Exception caught instantiating Forms report server extension: System.IO.FileLoadException: Could not load file or assembly 'CT.Integrations.SSRS.Web.Impl, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. The parameter is incorrect. (Exception from HRESULT: 0x80070057 (E_INVALIDARG))
File name: 'CT.Integrations.SSRS.Web.Impl, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' ---> System.ArgumentException: Invalid directory on URL.

Note, the DLL is purposedly not strong named as this an unfortunate ripple affect causing all referenced assemblies to also be signed.

The rssrvpolicy.config does have the following entry to hopefully allow for this:

<CodeGroup
class="UnionCodeGroup"
version="1"
Name="SecurityExtensionCodeGroup"
Description="Code group for the sample security extension"
PermissionSetName="FullTrust">
<IMembershipCondition 
class="UrlMembershipCondition"
version="1"
Url="C:\Program Files\Microsoft SQL Server\MSRS11.MSSQLSERVER\Reporting Services\ReportServer\bin\*.dll"/>
</CodeGroup>  

I have the DLL in both ReportManager\bin and ReportServer\bin folders.  What might cause this error?

Fusion logs show the dll loads successfully so not sure why SSRS is not happy.