This error looks like you did not activate any storage layer for the CmfBlockBundle. Do you have something like
cmf_block:
persistence:
phpcr:
enabled: true
If you also use the CmfCoreBundle, it is enough to have it enabled there, as the CmfCoreBundle prepends this configuration to all cmf bundles.
cmf_core:
persistence:
phpcr:
enabled: true