Data Center is being initialized after upgrade to RHEV 3.1

Issue

After a successful upgrade to RHEV 3.1, I installed rhevm-dwh and rhevm-reports (as indicated by the upgrade scripts) - both finished OK. As stated in the Admin Guide, I changed the compatibility version to 3.1 for the cluster Prod10G (the only cluster in datacenter) and for the datacenter. The following error appeared:

2014-Mar-17, 13:24 Failed to update Data Center PHX2. (User: rhevadministratoraccount)
2014-Mar-17, 13:24 Invalid status on Data Center PHX2. Setting status to Non-Responsive.
and then: 
2014-Mar-17, 13:28 Data Center is being initialized, please wait for initialization to complete.

• Last message repeats every few minutes.
• The compatibility versions are shown as "3.1" for both cluster and datacenter in Admin WebUI.