Are you Unable to reach Citrix License Server from XenCenter for your Xenserver pool?
We recently patched our Citrix servers and had to relicense them with a current license. We are running the latest windows server version of the Citrix license manager. We are running Citrix Xenserver 6.2 and some Xenapp farms. We have all the firewall rules in place required for the license server, most importantly is tcp port 27000. We verified we were able to connect to this port from the Xenserver hosts successfully.
However after installing the new license and going into Xencenter to activate the licenses we were getting the message that the license server could not be found. We spent a few days reviewing the issue, removing/re-adding the licenses, double checking the firewall rules and network connectivity, restarting the license server and services but could not activate the licenses. At this point we were a bit frustrated. Finally we decided to restart the toolstack on the pool master and each of the hosts in the pool to see if this might help.
After all the servers in the pool had the toolstack restarted we were successfully able to connect to the license server and activate the license. Anyway, this was the fix for us.
Give it a try and best of luck.