How do I resolve an "Error 10009: Unable to open Gurobi license file"?

The errors

Unable to open Gurobi license file 'C:\gurobi\gurobi.lic'
Unable to open Gurobi license file '/Library/gurobi1200/gurobi.lic

are most likely caused by Gurobi environment variables that are not set up correctly.

Please make sure that the system environment variable GRB_LICENSE_FILE points to a valid Gurobi license. To check the value of the environment variable, you can run echo $GRB_LICENSE_FILE (for Windows echo %GRB_LICENSE_FILE%).

Note: The system environment variable GRB_LICENSE_FILE must point to the exact location of the file. For example, if the license file gurobi.lic is in the directory D:\work, then GRB_LICENSE_FILE needs to be set as D:\work\gurobi.lic.

Other causes may be that:

• You don't have permission to read the license file.
• The license file has a hidden extension such as .txt or .rtf.

Further information

• Where do I place the Gurobi license file (gurobi.lic)?