It means gvmd needs to talk to a scanner through which NVT will be loaded. You have probably started gvmd with the option –osp-vt-update=/opt/gvm/var/run/ospd.sock or similar.
So you must have an OSP scanner like ospd-openvas listening to socket /opt/gvm/var/run/ospd.sock
You typically want to have this by running ospd-openvas through:
/opt/gvm/bin/ospd-scanner/bin/python3.6 /opt/gvm/bin/ospd-scanner/bin/ospd-openvas --pid-file /opt/gvm/var/run/ospd-openvas.pid --unix-socket=/opt/gvm/var/run/ospd.sock --log-file /opt/gvm/var/log/gvm/ospd-scanner.log --log-level DEBUG --lock-file-dir /opt/gvm/var/run/ --config /opt/gvm/etc/openvas/ospd.conf