Symptoms
It is not possible to create new Chunk Servers (CSes) or Metadata Servers (MDS) on the VHS 7.5 Update 5 nodes freshly added to the Vstorage cluster version VHS 7.5 Update 6 (where all other nodes are on version VHS 7.5 Update 6).
Cause
In Virtuozzo Storage it is recommended to add only the same version/build VHS nodes to the existing clusters, adding VHS nodes running the previous version/build is not recommended.
Resolution
If you need to add fresh nodes to the Virtuozzo Storage cluster running on VHS7.5 Update 6 , those new nodes should also run version VHS7.5 Update 6.