I've received this exception multiple times over the past few days:
PayPal.Exception.ConnectionException Invalid HTTP response The underlying connection was closed: An unexpected error occurred on a send.
PayPal.Exception.ConnectionException: Invalid HTTP response The underlying connection was closed: An unexpected error occurred on a send. at PayPal.HttpConnection.Execute(String payLoad, HttpWebRequest httpRequest) at PayPal.APIService.MakeRequestUsing(IAPICallPreHandler apiCallHandler) at PayPal.PayPalAPIInterfaceService.PayPalAPIInterfaceServiceService.SetExpressCheckout(SetExpressCheckoutReq setExpressCheckoutReq, String apiUserName)
I can't track down what's causing it - nor is there much information out there about the error.
This is happening when we initiate a request to PayPal to get an auth token back (so customers are never redirected to PayPal from our site).
The error seems to happen very infrequently - we run a busy site and the exception's only came through a few times and have taken many PayPal orders, so it's not affecting the majority of customers.
Thanks Steven