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Why do I receive License Manager Error -15?

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Why do I receive "License Manager Error -15"?
On the client system, the error appears as:
ERROR: License checkout failed. Cannot connect to license server. License Manager Error -15.
On the license server, the error appears as:
ERROR: FlexNet Licensing error: -15,10. System Error: 10061 "WinSock: Connection refused"

Accepted Answer

MathWorks Support Team
MathWorks Support Team on 6 Dec 2023
Edited: MathWorks Support Team on 6 Dec 2023
This error can have different meanings depending on which system it occurs.
If you receive this error on a client installation of MATLAB:
  1. If you require a Virtual Private Network (VPN) to connect to your company/school network that hosts the Network License Manager, make sure that you are connected to the VPN. 
  2. Verify communication by pinging the license manager server from the client with the following command: ping <hostname>  where <hostname> is the hostname of the server machine. If this fails you may have a networking error that is preventing the client from communicating with the license manager server. Contact your network administrator to resolve this issue. NOTE: If you know the IP address of the server and are able to ping that, the issue more lies within the DNS configuration of your network. You can replace the hostname in the server line of the network.lic with the IP address as a workaround
  3. Verify that the SERVER line of the network.lic on the client matches that of the license.dat file on the server itself. If the SERVER line differs it may cause the client to contact the wrong server/port.
  4. Check if there is a firewall(s) between the MATLAB client and the license manager server. The license manager communicates on two ports that must be opened through the firewall(s). These ports are specified in the license file hosted on the license manager server. If there is a firewall running, contact your System Administrator to open the necessary ports in the firewall.
If you receive this error on the license server:
  1. Verify that the license manager is running on the license server. If the license manager is not running, restart the license manager and try to run MATLAB again. This will often resolve the error. For more information on how to restart the license manager, see instructions:
  2. Verify that the TCP port numbers used by the license manager are not already being used by another application. To determine which port numbers the license manager is using, refer to the end of the SERVER and/or DAEMON lines in the license.dat file.
Note that the license manager uses two ports. The first port is used by lmgrd, and is defined at the end of the SERVER line in the license.dat file. By default, port 27000 is used. The second port is used by MLM, and is (optionally) defined at the end of the DAEMON line in the license.dat file. By default, the port is randomly selected.
SERVER Host_Name HostID 27000
DAEMON MLM <path/to/MLM> port=1711
Note: In this setup both the Host Name and HostID are from the License Server, not the client computer.
If the DAEMON line does not end with "port=<number>", then MLM is using a random open port. In the example above, you will need to check ports 27000 and 1711. Consult your network administrator for help identifying ports in use.
To verify which ports are in use on your system, you can use the "netstat" utility. This utility is called from the DOS prompt for Windows, or through a terminal window on Linux/MacOS. To use the utility, execute the following command:
netstat -aon
For Windows users: to then verify which program is using the port, copy the PID and then put it at the end of the command below:
tasklist | findstr
An example would be:
tasklist | findstr 21592
For more information about these ports, see the article below:
If you are getting this error while connected to a Wide Area Network (WAN), please see the article below:

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