There are 2 method you can try to fix the problem.
Method 1:
Please use " Run as administrator" to launch ZW3D, then reactivate it again. Even you already have the administrator authority.
Method 2:
The reason could be that the FlexNet Licensing Service hasn’t been successfully started. Try the following operations to start it manually.
1, Run-> service(Win7) / services.msc(XP).
2, To confirm whether there is FlexNet Licensing Service on Extended tab and its status is started. If its status isn’t started, please start it with manual method.
3, Run license manager with the administrator privilege to activate the license.