If you come across the above error,  you may also come across one or more of the errors below within your Citrix server event logs.

This computer running Citrix Presentation Server will now stop accepting connections. This server is no longer in or could not enter a licensing grace period.

Or

Citrix Presentation Server has entered the grace period. You have x hour(s) remaining before this server stops accepting connections from client devices

Or

The licenses required by this edition of MetaFrame Presentation Server are not present on the license server

Or

Citrix XenApp cannot contact the license server localhost

Or

This computer running Citrix XenApp will now stop accepting connections. This server is no longer in or could not enter a licensing grace period

Or

Error received while obtaining a license for a Citrix Presentation Server client connection. A grace license has been granted.

Or

Citrix presentation server license acquisition err (-xx): Unable to acquire a license from server. Please contact your system administrator or open event viewer for more details.
The alerts are generated when your citrix servers lose connection with the citrix license server. The citrix servers will continue to run until the grace period expires, unless they are able to communicate with the license server again.

Once your citrix servers have successfully communicated with the license server, you should receive the below or something similar within your event log.

This server is successfully communicating with the license server. Citrix Presentation Server has left the grace period

There are a few basic tasks you can carry out:

1) Ensure the citrix licensing services are running. If you need to locate you citrix license server, see link in step 3. If the license server is running go to step 2.

2) Restart the IMA service on your Citrix servers

3) If the above does not resolve issue, restart the license services on your Citrix licensing server. If you don’t know which server holds the citrix licensing role, see https://cloudbuild.co.uk/?p=1713

4) If any of the above do not resolve your issue, check your citrix licenses have not expired. On your Citrix license server, access Start, Programs, Citrix and Citrix license console. If they have expired you need to renew. Otherwise go to step 5.

5) From your citrix server, open a command prompt window and telnet to your citrix license server on port 27000. Please note, the port may be different, follow the link in step three to find out what port you are using. If you are unable to telnet to the port, you need to open the port on your firewall. The citrix servers need to communicate with the license server. Example telnet servername 27000

6) Can you ping the license server from a citrix server and the citrix server from the license server.

7) An incorrect Presentation Server edition level may have been set. Click a citrix server name within your citrix farm, from the right hand pane click set presentation server edition. Ensure the correct version is selected. Do the same for all your Citrix servers.

8.) Within a command prompt type netstat -a    –  Is the connection from your citrix server to license server established? If not you could have netoworking issues between servers.

9) Restart, the license server

10) If issue still exists, restart Citrix servers.

 Just a list of basic tasks which usually get to the bottom of grace period alerts.

Explanation from Citrix:

The problem occurs when there are intermittent problems, or delays (over 10 seconds per message) affecting the communication of messages between the XenApp server and the License Server. Once a timeout of a message sent from the XenApp server to the License Server occurs, subsequent communication to the License Server does not occur correctly because the persistent connection from XenApp to the License Server becomes unstable. As a result of the instability of this connection, subsequent user connections to the XenApp server might fail with the previously noted errors.

Important note: This problem only occurs in cases where the License Server is online and partially accessible over the network from the affected XenApp server. If the License Server is completely offline, this problem does not occur because the XenApp server continues to accept user connections until the standard licensing grace period expires or the License Server becomes accessible, whichever comes first.

A common source of this problem is intermittent network connectivity because of a physical problem such as damaged or defective network hardware (patch cables, patch panels, or switch ports).