This was the entry in my TNSNAMES.ORA file

XEL9DB =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = H1B-6F301-8Y49)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = xel9db)
)
)

But I am able to connect when I changed the entry to

XEL9DB =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = xel9db)
)
)

PAVB, Thank you very very much for the hint