Sql Developer (1.5.1) connection to RAC

Hello, I get a connection error

"Status : Failure -Test failed:lo exception: SO Exception was generated"

when connection type is TNS.

Here is extract from tnsnames.ora file;

TESTSPI =
(DESCRIPTION = (ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = <host_name>)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = <host_name>)(PORT = 1521))
(LOAD_BALANCE = yes) (FAILVOER = yes))
(CONNECT_DATA =
(SERVICE_NAME = oratest)
(failover_mode =
(type = select) (method = basic)
(RETRIES = 20) (DELAY = 5)) ) )

I can connect using sqlplus user/<password>@TESTSPI.

Any help gladly received.

Robert