Oracle Message NNO-00257 - warning: cannot get serial number from region store

ERRORwarning: cannot get serial number from region store
CAUSEThe server encountered an error while trying to get the configuration databases serial number. The error occurs almost always because time the server is unable to access the configuration database. If the error occurs during server startup, the server will shut down. If the error occurs during server operation (the server checks the serial number periodically to see if it should reload itself), then the server assumes a transient failure has occurred and repeats the operation a short while later. If the repetitions continue to fail for three days, the server will log another error and stop issuing the serial number load operation.
ACTIONFirst make sure that the Netadmin program has exported a server configuration for this name server. Next, make sure that the database is running, that its name and password as specified in the Oracle Network Manager are accurate, and that there is SQL*Net connectivity between the Oracle Names server and the database. If the error occurs during server startup, you can force startup anyway, with checkpoint data, by starting the server with the names.no_region_database parameter set to TRUE. If no checkpoint data is available, the server will shut down.