If your free licenses are not premium licenses,  they will be restricted to the device platform they were purchased for.

Are you 100% sure your free licenses are either premium licenses or licenses for Windows Mobile/CE ?   Are they subscription-based licenses? Or perpetual licenses and still within maintenance period?   Can you show a screenshot of the license info popup from your web-console, but without revealing your reg-code in the image?  

We successfully added Motorola MC45 and Wt41N0 in past. Now we would like to add also Dolphins, too. These are all Microsoft® Windows Embedded Handheld™ 6.5 devices. 

Your licenses look OK. 

As I do not have any Dolphin 60s to test out your flow of using MCBootstrapAgent.CAB and  bar-code generated by Ezconfig,  I could not comment on the enrollment flow.   I previously only used the old approach of generating agent binaries from agent builder in the web-console to enrol Windows CE/Mobile devices. 

As your licenses are OK and the warning message you got seems to suggest licensing problem,  I think you should open a support ticket directly with Soti Support team to further investigate.

The error mentioned by you is pointing towards the licence count so therefore, I would first request you to check for the number of available licences on Mobicontrol. You can however try to hit the update button on the License information tab to check for any updates in the license count and then try to see if you are able to add/ create a new device rule without this error.

But if still you are facing this issue, then there is a possibility that the extra license have been taken up by devices that were previously enrolled on to the MobiControl and then un-enrolled/ deleted by any chance but however, these are still not fully un-enrolled/deleted from the database which is resulting up in taking the extra license space. There is a way by which you can view all these devices on your database and make changes on to it by changing the device mode on database table (dbo.DevInfo).

But therefore, I would NOT encourage you to make any changes on the database yourself without taking a backup and I highly recommend you to go ahead and open up a case with soti support so that one of our expert agent can actually work on this with you.