ExactTarget Error: No results were received from the ExactTarget API

If you are working on extensive integration with ExactTarget from Dynamics CRM, then you might come accross this error message:"Error during send processing." "ExactTarget.MSCRM4.BusinessLogic.Connector.ExactTargetSendException: No results were received from the ExactTarget API. Send status is unknown. ---> ExactTarget.MSCRM4.BusinessLogic.Connector.ExactTargetSendException: No results were