This blog post shows one of the possibilities to resolve the error below in SSIS Web Service Task
[Web Service Task] Error: An error occurred with the following error message: “Microsoft.SqlServer.Dts.Tasks.WebServiceTask.WebserviceTaskException: The Web Service threw an error during method execution. The error is: Unable to connect to the remote server.
This can happen if your wsdl file is out dated. Save your wsdl file from your Web Service again.