Hi Nicolas,
There was a bug in oVirt [1] that in some cases a mac pool that doesn't support duplicate macs could get duplicates.
The bug was (hopefully) fixed.
The error that you see means that you have a mac pool that was affected by this bug and have duplicate macs although it doesn't support it.
The second part of the error should contain the list of the duplicate macs ("Following MACs violates duplicity restriction, and was pushed into MAC pool without respect to it:").
It is just a warning, you can ignore it.
But we advise you to go over the duplicate macs and fix them.
Alona.