In the web.xml file, the servlet-class to the callback service is com.google.checkout.jdk.CheckoutMessageHandlerServlet, whereas the actual class is in com.google.checkout.web.CheckoutMessageHandlerServlet . System returned servlet not found error. There is also another servlet definition with class com.google.checkout.sdk.CheckoutMessage for servlet CheckoutNotificationervlet. Such class does not exist.

The solution to this issue was to specify the servlet-class to the callback service as com.google.checkout.web.CheckoutMessageHandlerServlet in the web.xml file.