This error message indicates that an incompatible software is detected in your primary machine.
Please open the spacedesk Driver Console -> Diagnostics -> Incompatible Software, to check which software is present and just click the “Uninstall” button beside it then, reboot your primary machine before connecting a spacedesk viewer.
For further details, please check Troubleshoot -> Windows PC (Primary Machine) -> Incompatible Display Hook Driver Detected chapter in the user manual https://forum.spacedesk.netuser-manual/.