[i]ORCL81.WORLD =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = Oracle816)(PORT = 1521))
(CONNECT_DATA = (SERVICE_NAME = ORACLE81))
)

[/B]
Is that HOST is your system's name or the Home of oracle database location. If it was the second case, I would suggest that you change it to point to your host name. Make that change and try.

Here is an example:

ORCL81.WORLD =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = Your_host_name_here)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = Oracle816)
)
)

Hope this would fix the problem for you.

Good luck,
Sam