How to troubleshoot Citrix XenServer licensing
XenServer has been using the standard Citrix License Server since version 5.6. This can be a problem at times as there is an external license verification instead of the license file being applied to the XenServer host as in previous versions. The first thing to ensure is that the license file has been uploaded to the Citrix License Server by accessing it via the web page for it. Once you do indeed see the XenServer license file and what type it is (Platinum, Enterprise, etc.), we need to ensure that it is accessible via the XenServer host. To do this, you will need to go to the command line and use the standard ping command which uses ICMP. If ping is successful, you will want to use telnet command and specify the port of the license server, usually 27000. In most cases, resolving connectivity to the Citrix License Server will allow the successful license assignment. Should we be good with the above two network tests, you will need to use the standard “date” command and ensure that the day, month, year, and hopefully time is correct. If not, you may need to enter the BIOS of the host to update the hardware clock and/or configure NTP via the XenConsole.
To learn more and to read the entire article at its source, please refer to the following page, How to troubleshoot XenServer licensing- The Citrix Blogs