Demo has probably already expired for this or another application protected with same application signature and program id (since they are sharing same license data) on this computer.
You can change application signature and protect application again in order to get a clean start.
You can increase Update ID for this release and enable "Reset demo mode for this update" option in demo mode settings. New update will reinitialize demo limitations on remote computer if previous version is running as demo or it has already expired and is asking for activation code.
If you are testing different protection scenarios with PC Guard on your local machine you can use "Reset license" button in general project setting to reset license data on your computer.