I have not seen that error but the most common problems with respect to configuring the License Manager extension are:
1. The license manager server is not running on the default port 27000.
2. The server running ArcGIS Montitor does not have connectivity to the license manager server (firewall issue, no DNS name for the License Manager server, etc.).
Try running "lmutil.exe -h" from the command line to verify the file is not corrupted and you have permission to execute that file. See attached photo.
Next - trying connecting to your License Manager server by manually executing "lmutil.exe" from the command line where it is located in the ArcGIS Monitor "bin" directory:
lmutil.exe lmstat -s 27000@mylicensemanagerserver.esri.com -a -c @mylicensemanagerserver.esri.com
Where:
27000 is the default port number (the port number you expect your License Manager to be using
mylicensemanagerserver.esri.com = replace with your fully qualified license manager host name
You should see output similar to the following if the connection works.
Note the port number below in red; this number verifies the port number in use by your license manager server
lmutil - Copyright (c) 1989-2010 Flexera Software, Inc. All Rights Reserved.
Flexible License Manager status on Mon 11/25/2019 09:46
[Detecting lmgrd processes...]
License server status: 27000@mylicensermanagerserver.esri.com