I know when you get this error message there should be something wrong with the tnsnames.ora file... But in this perticular case I cannot find whats wrong, can some one help please.

I have pasted below is the text from tnsnames.ora file..
(ADDRESS = (PROTOCOL = TCP)(HOST = Oracle816)(PORT = 1521))

I have 3 machines.
1. Oracle816 which is a oracle 816 server.
2. test1.. which has oracle 816 client installed
3. test2.. which has oracle 805 client installed

System User Id and password for server is ora/ora.
***I have done find all tnsnames.ora file on all of these machines and made sure that they all have the same text pasted above.

I can login to sql plus or worksheet using ora/ora@orcl81
from test2 machine but I cannot do the same from oracle816 and test1 machine.
It gives me error saying..
TNS:could not resolve service name.
Where else is it looking for service name ?

Why ? this has really puzzled me !
Has anyone had this problem before, does anyone knows the solution ?
Thanks for all your help in advance