This error could be coming from 2 reasons: 
REASON#1: Make sure you have a LIVE internet connection when you were optimizing? i.e. required by Dirac Live software. 

REASON#2: Somehow, the Dirac Live license got corrupted. Please have a trial at Deleting the license file and re-open Dirac Live

a) Close Dirac Live 
b) Browse to 
For stereo version (DDRC-22/24)

For 8ch version (DDRC-88/nanoAVR)

c) Reopen Dirac live. reload your project and see if you can optimize now. 

Feel free to contact us if any questions.