I made some progress with integrating ASP.NET MVC3 & Google Checkout but I still cannot make the most basic call to the Checkout API. I think the problem is with my C# code now, because with all honesty, I do not understand how the code works exactly - I got the code from MSDN and tweaked it to add the necessary headers (required by the Checkout API). So if anyone could figure out what's wrong please step forward :)
The problem is explained on
StackOverflow