Intermittent JDBC connection

[teser3]

I am connecting to Oracle 10g RAC using JDBC in Tomcat 6.0.20.
It works around 50% of the time. When it doesnt work it shows this
error message:
IO exception: The Network Adapter could not establish the connection.

Here is my JDBC String:
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jdbcracle:thin(DESCRIPTION=(LOAD_BALANCE=on)
(ADDRESS=(PROTOCOL=TCP)
(HOST=170.11.5.111) (PORT=1521)) (ADDRESS=(PROTOCOL=TCP)
(HOST=170.11.5.112)
(PORT=1521)) (CONNECT_DATA=(SERVICE_NAME=service) (FAILOVER_MODE
=
(TYPE = SELECT) (METHOD = BASIC) (RETRIES = 180) (DELAY =
5) )))
jdbcracle:thin(DESCRIPTION=(LOAD_BALANCE=on)
(ADDRESS=(PROTOCOL=TCP)
(HOST=170.11.5.111) (PORT=1521)) (ADDRESS=(PROTOCOL=TCP)
(HOST=170.11.5.112)
(PORT=1521)) (CONNECT_DATA=(SERVICE_NAME=service) (FAILOVER_MODE
=
(TYPE = SELECT) (METHOD = BASIC) (RETRIES = 180) (DELAY =
5) )))
The above Description parameters I use in my tnsnames.ora and can
successfully connect to the Oracle RAC using SQL Plus with no issues.
I can also successfully ping to the IP addresses with no issues.
I also played around with the JDBC string and added (FAILOVER=ON) but
still have same issues.

Please advise.