Web服务调用... nullreference exception ...属性评估失败

Question

我尝试调用我的webservice，它给了我一个“nullreference exception”。这段代码以前有用。从通话中收到的状态代码是OK：200。可能发生了什么？

'** Shipping.Carriers is my web service
dim myWs as Shipping.Carriers
dim strCode as string

Using myWS = New Shipping.Carriers
    myWS.Credentials = System.Net.CredentialCache.DefaultCredentials

    '** when I pause here and check the status of the Web service...
    '** I see the Property Evaluation Failed on all of the functions in the web service

    myWS.Timeout = 400000

    '** the next line of code gives me the nullreference exception
    strCode = myWS.fUPS(my parameters go here)
    txtMsg.Text = strCode
End Using