When receiving this error it is almost always caused by an incorrect path. Check the Dispatch, and look at the Network path to see if it has been changed and is no longer correct. Keep in mind that when RRR processes an upload to a virtual alias it is not using the network path specified in the Send task configuration. It is using the network path that is embedded with the request from Dispatch, so ensure that the Dispatch path itself is correct and has not been changed.