Sorry to revive this topic but I will have to add this for future reference.
If you also set a different dblock size you will have to provide your --dblock-size as well. Otherwise you will also get above error when you try to restore without the local database. Example:
--blocksize=1MB
--dblock-size=200MB
(Thanks to mr-flibble for the workaround)
(Duplicati version 2.0.4.5_beta_2018-11-28)