This is most commonly caused by unusual characters in your name as found in your Pixologic ID profile.
To resolve, please do the following:
1. Log in.
2. Go to My Profile.
3. Look for any non-letter characters in your user name and remove them. For example, if your last name is "T'son" change it to "Tson" instead.
4. Enter your password.
5. Click Update to save the changes.
6. Go to your ZBrush folder. There, run the Pixologic License Manager.
- Note: ZBrush cannot be running when you do this.
- Note: Earlier versions called it the Pixologic Deactivation Manager
7. Select the ZBrush activation found there and click the Deactivate button.
8. Close that window, relaunch and reactivate ZBrush. You should be good from there. If you do continue to have trouble, please start a Support conversation to let us know.