The Client Agents cannot connect to the Task Server, not even the one on the Task Server itself.

In the Agent logs, the following error occurs:
Process: AeXNSAgent.exe (6428)
Thread ID: 8008
Module: AeXNetComms.dll
Source: AeXNetworkTransport
Description: Post to 'http://<Task Server IP>/Altiris/ClientTaskServer/Register.aspx?resourceGuid=<GUID>&lastResort=true' failed: Invalid data received in HTTP response. Expected <NUMBER> bytes, received 0 (-2147024883)

If this link is posted into a web browser, you will see the one of the following errors:

'HTTP-Error 500.19 - Error Message'

'HTTP-Error 500.23 - Internal Server Error' with the added message that 'the managed pipeline mode "integrated" is in use but not valid'

There is a misconfiguration in IIS

500.19 - The IIS user does not have proper privileges to read the Task Server files

500.23 - The managed pipeline mode is set to 'integrated' instead of 'classic'.

For Error 500.19

1. Browse to the Altiris\Altiris Agent Folder
2. Give read access to the IIS User, if you continue to get an error then check to make sure the privilege went to sub directories. If failure persists then give the Everyone group read access. 

For Error 500.23

1. Open the Server Manager
2. Select Roles > Web Server (IIS) > IIS Manager
3. Select your IIS Server and then Application Pools
4. Select the appPool that your asp.net app is running under
5. Click on 'Advanced Settings' from the right hand pane.
6. Under Advanced Settings > General > Managed Pipeline Mode, select "Classic"
7. Run IISRESET then have the client to check in with the task server

KB 171910  "Task Server is not registering to itself automatically"

KB 160948  "NS Client Task Agent fails to connect to itself"

KB 155009  "Task Server installed on Site Server is not registering to itself. Also clients don't register to it."

KB 165005  "Unable to register itself as a Task Server or unable to get package snapshots"