I got this error with every single host that we had previously in the old version of virtual center.  The way I got rid of it was to do the following as root on each esx box

rpm -qa | grep -i vmware-vpxa

then use that output and put it in the follwoing command

rpm -e filename from above

then issue the following

service mgmt-vmware restart

Then you are good to go.  You may add the host in virtualcenter.