The Task Server is trying to register itself as a Task Server.

When trying to access http://MyTaskServer.example.com/Altiris/ClientTaskServer/Register.aspx, they got a http error 404 Not Found.

As well when trying to reach http://MyTaskServer.example.com/Altiris/ they got the same problem.
When they tried http://MyTaskServer.example.com/Altiris/PS/ConnectionTest.html worked just fine.

Operation 'Head' failed. 
Protocol: HTTP 
Host: MyTaskServer.example.com:80 
Path: /Altiris/ClientTaskServer/Register.aspx 
Http status: 404 
Id: {####53EE-402C-400A-B698-#####067ED2A} 
Error type: HTTP error 
Error result: 0x80042D21 
Error code: 0 
Error note: HTTP status: 404 Not Found. The webpage cannot be found, the remote web server is down or URL is invalid 
Error message: HTTP error occured

The Application Event logs showed:

Event code: 3005 
Event message: An unhandled exception has occurred. 
Event time: 27/11/2017 20:15:00 
Event time (UTC): 27/11/2017 19:15:00 
Event ID: 7e8b2580aa344a35ba08a01c1b5411b3 
Event sequence: 1 
Event occurrence: 1 
Event detail code: 0 
 
Application information: 
    Application domain: /LM/W3SVC/1/ROOT/Altiris/ClientTaskServer-699-131562837001038011 
    Trust level:  
    Application Virtual Path: /Altiris/ClientTaskServer 
    Application Path: D:\progra~1\Altiris\Altiris Agent\Client Task Server\ServerWeb\ 
    Machine name: MyTaskServer 
 
Process information: 
    Process ID: 231892 
    Process name: w3wp.exe 
    Account name: IIS APPPOOL\Symantec Task Server AppPool 
 
Exception information: 
    Exception type: HttpException 
    Exception message: Failed to map the path '/altiris/clienttaskserver'.
   at System.Web.Configuration.ProcessHostMapPath.MapPathCaching(String siteID, VirtualPath path)
   at System.Web.Configuration.ProcessHostMapPath.System.Web.Configuration.IConfigMapPath2.MapPath(String siteID, VirtualPath path)
   at System.Web.Configuration.WebConfigurationHost.InitForConfiguration(String& locationSubPath, String& configPath, String& locationConfigPath, IInternalConfigRoot configRoot, Object[] hostInitConfigurationParams)
   at System.Configuration.Configuration..ctor(String locationSubPath, Type typeConfigHost, Object[] hostInitConfigurationParams)
   at System.Configuration.Internal.InternalConfigConfigurationFactory.System.Configuration.Internal.IInternalConfigConfigurationFactory.Create(Type typeConfigHost, Object[] hostInitConfigurationParams)
   at System.Web.Configuration.WebConfigurationHost.OpenConfiguration(WebLevel webLevel, ConfigurationFileMap fileMap, VirtualPath path, String site, String locationSubPath, String server, String userName, String password, IntPtr tokenHandle)
   at System.Web.Hosting.ApplicationManager.CreateAppDomainWithHostingEnvironment(String appId, IApplicationHost appHost, HostingEnvironmentParameters hostingParameters)   at System.Web.HttpRuntime.HostingInit(HostingEnvironmentFlags hostingFlags, PolicyLevel policyLevel, Exception appDomainCreationException)
 

ITMS 7.6, 8.x

We found out that in IIS these virtual directories, Altiris and Client Task Server, had this path:
D:\progra~1\Altiris\Altiris Agent\Client Task Server\ServerWeb\

For some reason IIS was not able to resolve "D:\progra~1" as a valid path.

1. Check the path on the virtual directories in IIS (e.g. Default Website>Altiris>Client Task Server). Fix the path under "Basic Settings" on the right pane in IIS Manager after selecting the virtual directory to be the full path name: D:\Program Files\Altiris\Altiris Agent\Client Task Server\ServerWeb\ .
2. Run IISRESET.
3. Try again the desired pages.
4. Let the agent try registering again.

Note: In case that after making the changes in the IIS virtual directories, if after restarting the Task and Agent services, the path goes back to D:\progra~1\Altiris\, then go to the registry and change this reference to the full path under the HKLM>Software>Altiris keys.
Restart the agent and task services and run IISRESET and check that the path stays as desired.