Flex invalid session error - actionscript-3

Question

Am trying to call a service running in tomcat through remote objects from flex, when i call the remote object it throws flex invalid session error
Channel.Ping.Failed error There was an unhandled failure on the server. The FlexSession is invalid. url: 'http://localhost:8080/Server/messagebroker/amf/'
[RemoteObject destination="reinforcementService" channelSet="[ChannelSet null ]"]
Send failed
Code
<s:CallResponder id="getReinforcementsResult"/>
<services:ReinforcementService id="reinforcementService" fault="Alert.show(event.fault.faultString + '\n' + event.fault.faultDetail)" showBusyCursor="true"/>
<s:RemoteObject id="ro2" destination="reinforcementService" endpoint="{parentApplication.serviceURL}" result="ro2_resultHandler(event)" fault="ro2_faultHandler(event)"/>
and i call the method using
ro2.getReinforcements();
and i disconnect the remote object in result handler to avoid DuplicateFlexSessions error
ro2.disconnect();
and the channel definition in services-config.xml is as follows
<channel-definition id="my-amf" class="mx.messaging.channels.AMFChannel">
<endpoint url="http://{server.name}:{server.port}/{context.root}/messagebroker/amf" class="flex.messaging.endpoints.AMFEndpoint"/>
<properties>
<polling-enabled>true</polling-enabled>
<add-no-cache-headers>true</add-no-cache-headers>
<!-- <invalidate-session-on-disconnect>true</invalidate-session-on-disconnect> -->
<invalidate-session-on-disconnect>true</invalidate-session-on-disconnect>
</properties>
</channel-definition>
how to solve this problem?