C# - Authentication To FreshBooks Via DotNetOpenAuth?

I'm trying to use OAuth for authentication for the FreshBooks API from my ASP.NET MVC C# app. Here is what I have so far: I'm using DotNetOpenAuth here is the code I have in my controller action

if (TokenManager != null)
{
ServiceProviderDescription provider = new ServiceProviderDescription();[code].....


The TokenManager is the same class that is provided with the DotNetOpenAuth sample, I've set my consumer secret that FreshBooks gave me.On the consumer.Channel.Send(consumer.PrepareRequestUserAuthorization(...)) I've got the following exception:

"The remote server returned an error: (400) Bad Request.".Am I doing this correctly? Based on FreshBooks documentation and DotNetOpenAuth samples that should work correctly. Is there a simpler way to authenticate with OAuth, as DotNetOpenAuth is a bit huge for simply using OAuth authentication?