I am running a LAB 1 dell PE 2950 Stand alone esxi 6 server then 2 Dell PE 610 Server running in a cluster under ESXi6 and vCenter6 ( trial ) some how my cluster is out of sync with what Fault Tolerance ( Legacy) mode one is in vs. the other so I really don't have a usable Cluster.
ESXi6-02 reports Supported (5.0.0-5.0.0-5.0.0)
ESXi6-03 reports Supported (6.0.0-6.0.0-6.0.0)
I can't see where to change this setting at all in Vcenter6. I know it should match as they were loaded off teh very same .IOS ESXi6
Photos for info -- lol Pictures work 10,000 words
But as i can see your esxi 6-02 is running with esxi host 5.5.0 which will show you the error like this. its obvious.