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."
Cause
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.
Solution
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.