ORA-17629: Cannot connect to the remote database server ORA-17627: ORA-12154: TNS:could not resolve the connect identifier specified

Error :

RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of Duplicate Db command at 07/21/2015 10:06:15
RMAN-05501: aborting duplication of target database
RMAN-03015: error occurred in stored script Memory Script
RMAN-03009: failure of backup command on c1 channel at 07/21/2015 10:06:15
ORA-17629: Cannot connect to the remote database server
ORA-17627: ORA-12154: TNS:could not resolve the connect identifier specified
ORA-17629: Cannot connect to the remote database server

Source : PROD (Target in RMAN term)

Target : CLONE (Auxiliary in RMAN term)

Cause :

- I was getting this error during RMAN duplicate

- Target instance tnsnames entry was missing in source tnsnames.ora

Fix :

- Make sure you have both tnsnames entries in both source and target oracle home in tnsnames.ora  under $TNS_ADMIN

- You must be able to do tnsping from both the servers for both target (SOURCE) and auxiliary (TARGET) instances.