Symptoms
An ESXi/ESX host in vCenter Server reports the error:

Unable to apply DRS resource settings on host. The operation is not allowed in the current state. This can significantly reduce the effectiveness of DRS.
WARNING: UserDuct: 184: Cannot allocate a new data segment, out of memory
 Resolution
Note: The resolution in this article works only if your environment does not include NSX or VMware Horizon View or VSAN. To resolve this issue if your environment includes NSX/View/VSAN, contact VMware Support.

This warning does not have any impact on production and can be safely ignored.

To resolve this issue, restart the management agents (hostd and vpxa) on the host.

If the problem persists after restarting the management agents, remove the host from the cluster and then re-add it to the cluster:
  1. Place the host into maintenance mode.

    Note: If DRS does not migrate the virtual machines to other hosts, migrate them manually.
     
  2. Ensure that there are no virtual machines running on the host.
  3. Remove the ESXi/ESX host by dragging it out of the cluster.
  4. Re-add the ESXi/ESX host by dragging it into the cluster.
  5. Exit from maintenance mode.
 Update History
07/12/2012 - Added ESXi 5.0 and vCenter Server 5.0 to Products
01/16/2013 - Added ESXi 5.1 and vCenter Server 5.1 to products
02/22/2013 - Added WARNING symptom
03/20/2013 - Removed vCenter version 4.1 in symptoms section as it is applicable for all versions
07/28/2015 - Added 6.0 products