Why do I receive License Manager Error -4?

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When I try to start MATLAB or use a toolbox, I receive the following error:
ERROR: License Manager Error -4
Maximum number of users for MATLAB reached. Try again later
What does this error mean and how can I resolve it?

Accepted Answer

MathWorks Support Team
MathWorks Support Team on 16 Sep 2022
Edited: MathWorks Support Team on 16 Sep 2022
This error indicates that all licenses are currently in use. This means that all of the keys for a particular product have been checked out from your license server. You will not be able to access a license for the product until another user has returned the license back to the pool. For information about the current licenses in use you can check with your License Administrator. Your License Administrator can check the usage of licenses by following the instructions in the License Administrator Section below.
This error can also occur if there is a misunderstanding as to what products are owned. For example, if the Network License Manager has a 2 licenses for MATLAB R2022b and 3 seats for MATLAB R2021a, then 5 seats could check out R2021a and older, but only 2 seats could check out R2022b. Trying to checkout a third seat would result in an error -4.
License Administrator Section
1) Launch LMTOOLS, located within the $MATLAB\etc\win64. If lmtools.exe is not in that folder, see the related solution "Why are necessary license manager scripts missing from my license manager directory?" below.
2) Click the "Perform Status Enquiry" button on the SERVER STATUS tab to get a full report of the current license usage.
For Linux/Mac:
1) Open a terminal Window. For Mac OS X, use the Terminal application located in the Applications/Utilities directory.
2) In the terminal, change directories to the $MATLAB/etc directory. For example:
cd /usr/local/MATLAB_R2022a/etc
Mac OS X
cd /Applications/MATLAB_R2022a.app/etc
3) Run the following command to get the usage information
./lmstat -a -c license.dat
An example output from LMTOOLS or lmstat is located below:
Flexible License Manager status on Mon 9/26/2022 15:35
[Detecting lmgrd processes...]
License server status: 27000@license1
License file(s) on license1: C:\Program Files\MATLAB\R2022b\flexlm\license.dat:
license1: license server UP (MASTER) v11.18.1.0
Vendor daemon status (on license1):
MLM: UP v11.18.1.0
Feature usage info:
Users of MATLAB: (Total of 2 licenses issued; Total of 2 licenses in use)
"MATLAB" v22, vendor: MLM
nodelocked license, locked to "ID=123456"
joesmith joe-pc joe-pc (v22) (joe-pc/27000 102), start Mon 9/28 15:37
janedoe jane-pc jane-pc (v22) (jane-pc/27000 101) start Tues 9/29 08:26
In this example, a license would not be available until either Joe or Jane closes MATLAB to return the license.

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