i think it was one of my largest problems in oracle 9i
when i setup the oracle 9i on network, most of the time i found the error message ora12535
finally after 4 days i found the solution, the error itself was trivial but because of the short explanation of oracle error messages.
the problem is the client can't connect to the server will the ping is working.
the error was in windows xp sp 2 which closes all of the ports.
the gem is :you can turn off the firewall of the windows or you can a port 1521(or your oracle port)to the exceptions.
how did i get to this if you are interested:-
from the client you write in ms dos window the command>tnsping TheHostName
host name of your server then if it did will so no error in the network or ports
and you can get the host from the returned message.
or if it returned time out error
so there is a problem in the port or network
if error still appears
i am happy to receive your questions and may Allah help all of us
thank you all and thanks for this site creators