Oracle Listener problem TNS-12518

[oraclevijay]

Dear Oracle Experts,

I am facing a continuous problem in oracle production database.I got the below error messages in listener.log


TNS-12518: TNS:listener could not hand off client connection
TNS-12560: TNSrotocol adapter error
28-MAR-2009 21:18:22 * (CONNECT_DATA=(SERVER=DEDICATED)(SID=acl)(CID=(PROGRAM=)
(HOST=ipmon01.americanstandard.ip-soft.net)(USER=ipmon))) * (ADDRESS=(PROTOCOL=tcp)
(HOST=170.205.13.22)(PORT=51551)) * establish * acl * 12518
TNS-12518: TNS:listener could not hand off client connection
TNS-12560: TNSrotocol adapter error
......
continuosly coming....like this


my temporary solution is just restarting the listener
and the error again comes within in a couple of hours..


my oracle database configuration is
oracle 10.2.0.4 WINDOWS recently upgraded from 9.2.0.5 without applying any patch


RAM 8 GB
ORACLE USAGE 1.324GB
available free physical memory 6gb
only one database installed in server.

os MICROSOFT WINDOWS SERVER 2003 R2 ENTERPRISE EDITION SERVICE PACK 2

SERVER DEDICATED
DIRECT_HANDOFF_TTC=off
server has intial 3gb and maximun 4gb virutal memory

sga_target='1100M'
pga_aggregate_target='750M'
sessions=335
processes=300
transactions=368
large_pool_size=0

Server is in Automatic Storage Management

when number of sesssion increased to 75 and above
i am getting ths error

In the downtime of database , i have altered sga_target=800mb and pga_aggregate_target=700mb after a couple of days i am again facing the error

please,anybody can share u r ideas
Thanks in Advance
Vijay.S

[PAVB]

oerr TNS 12518
12518, 00000, "TNS:listener could not hand off client connection"
// *Cause: The process of handing off a client connection to another process
// failed.
// *Action: Turn on listener tracing and re-execute the operation. Verify
// that the listener and database instance are properly configured for
// direct handoff. If problem persists, call Oracle Support.
// *Comment: The problem can be worked around by configuring dispatcher(s)
// to specifically handle the desired presentation(s), and connecting
// directly to the dispatcher, bypassing the listener.