MSXML problems
Issue
The Arellia or NS/SMP agents have communication issues when everything appears correctly configured and the NS/SMP server is accessible via a browser session which uses anonymous access. If communication testing to postevent (http://<servername>/altiris/ns/postevent.asp for NS 6. http://<servername>/altiris/ns/agent/postevent.aspx for SMP 7.x.) works with an authenticated browser session then the issue is usually NTFS permissions on folders or files which the agents need to access.
An example agent log message is:
<event date='Jan 06 18:22:46' severity='1' hostName='Client673' source='FileInventoryAgent' module='ArelliaFileInvAgent.dll' process='AeXNSAgent.exe' pid='2520' thread='1396' tickCount='4428062' >
  <![CDATA[Failed to process policies from server 'Server14.test.local'>]]></event>
Resolution
With NS 6:
Reregister MSXML 2 and 3. If MSXML 2 doesn't register or doesn't exist that should not be a problem.
    - from a command line in the \system32 directory type the following and then hit enter: regsvr32 msxml2.dll
    - from a command line in the \system32 directory type the following and then hit enter: regsvr32 msxml3.dll
With SMP 7:
Reregister MSXML 6.
    - from a command line in the \system32 directory type the following and then hit enter: regsvr32 msxml6.dll