Message Oracle NNC-00003 - error opening stream string

ERRORerror opening stream string
CAUSEA name server or client program attempted to open a connection to another server and failed, either because the server is down, or because the network path to that server is not working. This error is usually displayed underneath an error which describes the problem in more detail.
ACTIONMake sure that the server being connected to is listening on the address used, and that there is network connectivity between the two end-points.