Oracle Database Discussions

Hello All,
I have a rac 11.2.0.1 database with 2 node cluseter.
I have a strange problem that when connecting from client using Toad, sql developer or sql plus session I get ORA-12514: TNS: listener could not resolve SERVICE_NAME error at times. but when I connect from the database server using the service name I can connect successfully. I can also connect from different database server using the service name but only from a client access at times I see ORA-12514 error. Then I wait for 10 to 15 mins, attempt to connect works fine.
I am not sure what to fix as when I do lsnrctl status on both the nodes, all the services are up. Below is cluster config and listener.ora contents from node1.

[oracle@rs1pre91dvdba01 ~]$ nslookup rs1pre91cl
Server: 172.30.1.25
Address: 172.30.1.25#53

Name: rs1pre91cl.pre.ccosvc.com
Address: 172.30.2.221
Name: rs1pre91cl.pre.ccosvc.com
Address: 172.30.2.222
Name: rs1pre91cl.pre.ccosvc.com
Address: 172.30.2.223

[oracle@rs1pre91dvdba01 ~]$ cat /u01/app/11.2.0/grid/network/admin/listener.ora
LISTENER=(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=IPC)(KEY=LISTENER)))) # line added by Agent
LISTENER_SCAN3=(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=IPC)(KEY=LISTENER_SCAN3)))) # line added by Agent
LISTENER_SCAN2=(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=IPC)(KEY=LISTENER_SCAN2)))) # line added by Agent
LISTENER_SCAN1=(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=IPC)(KEY=LISTENER_SCAN1)))) # line added by Agent
ENABLE_GLOBAL_DYNAMIC_ENDPOINT_LISTENER_SCAN1=ON # line added by Agent
ENABLE_GLOBAL_DYNAMIC_ENDPOINT_LISTENER_SCAN2=ON # line added by Agent
ENABLE_GLOBAL_DYNAMIC_ENDPOINT_LISTENER_SCAN3=ON # line added by Agent
ENABLE_GLOBAL_DYNAMIC_ENDPOINT_LISTENER=ON # line added by Agent
[oracle@rs1pre91dvdba01 ~]$


Please can I get help in understand what is problem and how to fix it.

Thanks