Re-install Diamond Programmer 3.12 and try again. Contact Lattice Semiconductor if the problem persists. 

 

Solution: 

Try to install the base SW first then the 3.12 SP1 encryption pack by clicking the Diamond Programmer Standalone 3.12 link below: https://www.latticesemi.com/view_document?document_id=53114

Refer also to FAQ-5925