Database Software

hello, i need your help

I´m trying to configure a connection from my oracle client 10g in Windows XP with a Oracle Rac Database 10G R2. The cluster database have 2 nodes, when i put the connection string in the TNSnames.ora file in the side my oracle client, i achieve connect the first time, but, de second time not success because appears the error "ORA-12545: the connection failed because the host destiny or the object don´t exist". I'm triyig to fix this error and I'm reding articules about connections, bust i don´t resolve the problem.

The connection string in the TNSnamse. ora in the side client and the side servers nodes of cluster is it:

PR_TAF =
(DESCRIPTION =
(ENABLE = BROKEN)
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = A.B.C.D)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = A.B.C.D)(PORT = 1521))
)
(LOAD_BALANCE = ON)
(FAILOVER = ON )
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = pr_taf)
(FAILOVER_MODE =
(TYPE = SELECT)
(METHOD = BASIC)
(RETRIES = 180)
(DELAY = 5)
)
)
)