Is there any config variable somewhere which is limiting the max call limit on FS to 1000?

Set-up:
Taking FS for max call load on my machine.

User freeswitch is calling internal gateway and playing demo-ivr

User freeswitch defined in vars.xml
<X-PRE-PROCESS cmd="set" data="default_provider=10.60.20.145"/>
<X-PRE-PROCESS cmd="set" data="default_provider_username=freeswitch"/>
<X-PRE-PROCESS cmd="set" data="default_provider_password=freeswitch"/>
<X-PRE-PROCESS cmd="set" data="default_provider_from_domain=10.60.20.145"/>

<X-PRE-PROCESS cmd="set" data="default_provider_register=false"/>
<X-PRE-PROCESS cmd="set" data="default_provider_contact=5000"/>

Internal Gateway defined in directory/default/freeswitch.xml
<include>
<user id="freeswitch">
    <params>
      <param name="password" value="freeswitch"/>
      <param name="vm-password" value="5000"/>
    </params>
    <variables>
      <variable name="toll_allow" value="domestic,international,local"/>
      <variable name="accountcode" value="5000"/>
      <variable name="user_context" value="default"/>
      <variable name="effective_caller_id_name" value="Extension 5000"/>
      <variable name="effective_caller_id_number" value="5000"/>
      <variable name="outbound_caller_id_name" value="$${outbound_caller_name}"/>
      <variable name="outbound_caller_id_number" value="$${outbound_caller_id}"/>
      <variable name="callgroup" value="techsupport"/>
    </variables>
</user>

After 1000 calls, it is giving the same error
-ERR DESTINATION_OUT_OF_ORDER

Yes, my CPU (quad-core AMD) and RAM (2GB only) are under heavy stress by the time 1000 calls are being done, but is it not a little strange that every time the resources get exhausted at precisely 1000 calls!

regards,
Anita