I have seen this error since I upgraded to vSphere 5.5 last week. There is a kb article here on how to fix this. According to this kb article this is a known issue in vCenter 5.5. I am using the vCSA (vCenter Server Appliance) and it is affected as well. So I just wanted to share what to do based on the KB article.
Screenshot of the error.
Open putty and ssh to your vCSA and execute the following.
cp vpxd.cfg vpxd.cfg.orig
Now scroll down to the line before </vpxd> and insert the following code from the kb article referenced above.
Now restart vCenter Server Service
service vmware-vpxd restart
Now after the services have restarted all should be good.