Follow the info on how to transfer certs between the DCE and NetBotz or how to use no verification.
Additionally, I have noticed that in DCE if you have too many wild cards when it comes to this part:
Device menu --> NetBotz Appliance Communication Settings --> NetBotz Appliance Credentials
It may not work. I recommend adding an individual entry with the specific IP of the unit you're having an issue with.
Additionally, if you have added a secondary user and are using that user instead of superuser for the "NetBotz Appliance Credentials" in DCE, please make sure that this user has logged into the NetBotz appliance directly at least once.