The customer moved the Symantec Management Agent (aka Altiris Agent) from the C: drive to the E: drive. After that they started seeing this error message in the Agent UI:
"Package Server is configured to publish http(s) codebases, but could not access it's own web site"

The Agent logs shows messages like this:

<event date='07/10/2018 01:09:31.2870000 +08:00' severity='1' source='Package Server Agent' module='AeXNSCPackageServer.dll' process='AeXNSAgent.exe' pid='6764' thread='6004' tickCount='243286953' >
<![CDATA[Package Server could not access own Web Site using HTTP, although it is configured to serve it. The HTTP requests from clients cannot be served. See logs for detailed failure reason. (health state: 0x00000311).]]>
</event>

Looking at the agent logs we noticed that the agent was not able to reach out his own link for the connection test:
HTTPS://Siteserver02.example.com/Altiris/ConnectionTest.html

When we tried to open the link in his browser we got:
HTTP Error 500.19 - Internal Server Error

The requested page cannot be accessed because the related configuration data for the page is invalid.

Error Code
0x80070005

Config Error
Cannot read configuration file due to insufficient permissions

Config File
   \\?\E:\Program Files\Altiris Agent\Package Server Agent\web.config

Package Server could not access own Web Site using HTTPS, although it is configured to serve it. The HTTPS requests from clients cannot be served. See logs for detailed failure reason. (health state: 0x00001331).
-----------------------------------------------------------------------------------------------------
Process: AeXNSAgent.exe (3512), Thread ID: 7104, Module: AeXNSCPackageServer.dll
Priority: 1, Source: Package Server Agent

OR

Package Server could not access own Web Site using HTTPS, although it is configured to serve it. The HTTPS requests from clients cannot be served. See logs for detailed failure reason. (health state: 0x0000311).
-----------------------------------------------------------------------------------------------------
Process: AeXNSAgent.exe (6764), Thread ID: 6004, Module: AeXNSCPackageServer.dll
Priority: 1, Source: Package Server Agent

ITMS 7.6 HF7, 8.x