Ensure that you are using the correct license server.

If you were originally using your local machine as the license server, ensure that Houdini is not using SideFX as the license server.

Launch the License Administrator and navigate to the top right corner drop down menu, under the login option.

1. Select "Switch to on-premise license server (sesinetd)" (H21.0.599 and up) or "Use Enterprise Servers" (until H21.0.512).
   
   
   

2. Move your local machine (Local Server) by pressing the + button from "Found Server(s)" section to the top section, and click on the UPDATE button at the bottom.
   

3. Ensure your local machine is set as the primary license server.

If you were originally using SideFX as the license server (login-based licensing), ensure that you are now not using your local machine.

Launch the License Administrator and navigate to the top right corner drop down menu, under the login option.

Select "Switch to Online Licensing (SideFX Login)". You may be prompted to log into your SideFX account if are not logged in.