If you use the Pervasive.SQL License Administrator to enter a new Pervasive.SQL license key, you may get the message
DBU - Access Denied
when clicking on Apply Licence Key
This would appear to be a bug in the Pervasive.SQL components locking certain parts of the Pervasive.SQL setup during installation.
The simplest way of resolving this issue is to reboot the server that Pervasive.SQL is installed on. Once the server has rebooted, you are then able to enter your license key correctly.
Other methods can be viewed on this external site