You follow the steps in related article HOWTO80780 to upgrade your Symantec Endpoint Protection (SEP) client software with AutoUpgrade. You opt to download the client installation package from a web server that is accessible from the systems you wish to upgrade, by clicking the "Download from the following URL (http or https)" option and entering the URL of the package.
After adding the client installation package, clients normally check in at the next heartbeat interval and will know to start the upgrade process, downloading the package to %temp%. However, you find that this does not happen, with %ProgramData%\Symantec\Symantec Endpoint Protection\CurrentVersion\Data\Logs\cve.log showing the specific exception in the Error section below.
[YYYY-MMM-DD HH:MM:SS.ssssss] [ERROR] cve::SylinkCommunicatorImpl::FetchUpgradePackage: Unknown exception occurred for autoupgrade from myserver\some_location\setup.exe
This issue will occur if there is a client licensing issue.
Click the Related Articles button on the right. Use the provided articles to review your license status and resolve any related issues, prior to deploying Sylink to the clients and attempting AutoUpgrade again.