You added more seats to your Network license and the number of allowed clients on the Keyserver is not updated :

• Make sure you followed all the steps of this article
• On the Keyserver, click on Stop, then on Update, and then on Start

If it doesn't work on Windows, please follow these steps :

• Deactivate the license
• Quit the Keyserver app
• Go to C:\ProgramData\Abvent\com.abvent.KeyServerxxx and delete the registration file

• Open Regedit, go to HKEY_LOCAL_MACHINE\SOFTWARE\Abvent\Artlantisx\Artlantisxxx\Preferences and delete com.abvent.KeyServerxxx.60 file

• Empty the dustbin
• Restart the server
• Restart the Keyserver and reactivate the license again