When working with Ado.Net data services you may get following error.

Could not load file or assembly 'System.Data.Services.Client, Version=3.5.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' or one of its dependencies. The handle is invalid. (Exception from HRESULT: 0x80070006 (E_HANDLE))

This error can indicate anything related to JIT-er. In my case there is directly nothing to do with JIT-er.
I have a service which talks to database by using of ADO.NET services (like described in this post).

However my DataService overrides the method OnStartProcessingRequest. Within this method I invoke sometimes another service to check the caller’s permissions. If this fails the error shown above will appear.

In fact, this error is shown (at least) if the method like OnStartProcessingRequest fails during execution.

protected override void OnStartProcessingRequest(ProcessRequestArgs args)
{

  throw Exception(“Any error here causes the error described aabove”)

}

Read the complete post at http://developers.de/blogs/damir_dobric/archive/2010/01/26/dataservices-0x80070006-error.aspx