Why did I get the error "A project with an output type of class library cannot be started directly" with the ASP.NET SDK?
You got an error message - "A project with an output type of class library cannot be started directly."
This error occurred because the ASP.NET samples included with the SDK were built as a Class library and not an ASP.NET web application. You can't run the sample in debug mode and step through it as is.
Create your own ASP.NET web application referencing paypal_base.dll if you want the ability to step through your solution in debug mode. You can look to the code in PayPalAPI.cs to see how to use the SDK (paypal_base.dll) to make an API call.