Calling unmanaged DLLs in C# Web Application VS2008

I have a web app that calls some old unmanaged code.

I wrote a C++ managed class library to wrap calls to the older unmanaged DLLs.

This application worked fine in Visual Studio 2003

Now I've updated the class library to build in VS2008 but when running the Web App I get errors complaining of  FileNotFoundException.

The C++ class lib is added as a reference and all associated dependencies are located in bin directory.

I tried testing the class library with a simple console app and it works fine but when the web app starts to load it always fails.

Any ideas???? 

Below is a stack trace from the web app

[FileNotFoundException: The specified module could not be found. (Exception from HRESULT: 0x8007007E)]
   System.Reflection.Assembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, Assembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFo ...