Comment 3 for bug 1490361

I had the same issue after upgrading nova components.
The issue was that nova-conductor and nova-compute services did not use the same version.

I upgraded using apt-get upgrade but it didn't seem to update nova-conductor. After a apt-get -f upgrade nova-conductor the nova-conductor package was upgraded to same version as nova-compute and then it worked. Confirm by checking the package versions (dpkg -l | grep nova).