Clients does not contact the OCS server

Good morning, some computers not contacted the OCS server.

this computer is recorded only when you install the Agent.

I Attach the log file

==============================================================================
Starting OCS Inventory NG Agent on Friday, May 27, 2016 14:50:00.
AGENT => Running OCS Inventory NG Agent Version 2.1.1.1
AGENT => Using OCS Inventory NG FrameWork Version 2.1.1.1
AGENT => Loading plug-in(s)
    DLL PLUGIN => Searching for Plug-in DLL(s) in folder <c:\Program Files (x86)\OCS Inventory Agent\plugins>
    DLL PLUGIN => 0 DLL Plug-in(s) succesfully loaded on 0 DLL(s) found
AGENT => Using network connection with Communication Server
    COM PROVIDER => Loading Communication Provider <c:\Program Files (x86)\OCS Inventory Agent\ComHTTP.dll>
AGENT => Using Communication Provider <OCS Inventory NG cURL Communication Provider> Version <2.1.1.1>
AGENT => Sending Prolog
    DID_CHECK => Read DeviceID <NI75958-2016-05-27-11-45-35> and MACs <90:xx:xx:xx:xx:xx> in file <ocsinventory.dat>
    COM SERVER => Initializing cURL library for sendRequest
    COM SERVER => Using cURL without server authentication
    COM SERVER => Disabling cURL proxy support
    COM SERVER => Enabling cURL SSL server validation support using CA Bundle <C:\ProgramData\OCS Inventory NG\Agent\cacert.pem>
    COM SERVER => Sending HTTP Post request to URL <https://xxxxxx/ocsinventory>
    COM SERVER => HTTP Post response received <HTTP Status Code #200>
    COM SERVER => Cleaning cURL library
================= TRACE START ===============
<?xml version='1.0' encoding='UTF-8'?>
<REPLY>
  <OPTION>
    <NAME>REGISTRY</NAME>
    <PARAM NAME="Java Version W7" REGKEY="SOFTWARE\Wow6432Node\JavaSoft\Java Runtime Environment" REGTREE="2">CurrentVersion</PARAM>
    <PARAM NAME="Java Version XP" REGKEY="SOFTWARE\JavaSoft\Java Runtime Environment" REGTREE="2">CurrentVersion</PARAM>
    <PARAM NAME="SvcHost" REGKEY="SOFTWARE\Microsoft\Windows NT\CurrentVersion\svchost" REGTREE="2">netsvcs</PARAM>
    <PARAM NAME="VNC_Accept" REGKEY="SOFTWARE\VNC" REGTREE="2">Install</PARAM>
  </OPTION>
  <OPTION>
    <NAME>DOWNLOAD</NAME>
    <PARAM FRAG_LATENCY="10" PERIOD_LATENCY="1" ON="1" TYPE="CONF" CYCLE_LATENCY="60" TIMEOUT="30" PERIOD_LENGTH="10" EXECUTION_TIMEOUT="120" />
  </OPTION>
  <RESPONSE>STOP</RESPONSE>
  <PROLOG_FREQ>1</PROLOG_FREQ>
</REPLY>

================= TRACE STOP ===============
AGENT => Prolog successfully sent
SUPPORT => No support detected, Registration key : N/A
ERROR *** AGENT => Failed to write Prolog Frequency <Error code 5 = Accesso negato.  >
AGENT =>  Communication Server ask for Package Download
    DOWNLOAD => Package history file cleaning not required
DOWNLOAD => Download and setup tool successfully started
AGENT => Unloading communication provider
AGENT => Unloading plug-in(s)
AGENT => Execution duration: 00:00:00.

Thank you very much!