For Windows
Please add the path of glpsol.ext to your Environment variables.
1. Open the Control Panel
2. Click System
3. Click Advanced system setting
4. Open Environment variables
5. Edit Path
6. Add variable value ";the path where glpsol.exe locate" (e.g. ;D:\glpk-4.45\w64)
For Linux/Mac
Please follow the official GLPK document contained in each GLPK distribution.