Yesterday I was talking to a customer,that had a problem, after they had run a remediate on a ESXi 5.5 host, and it was upgraded/patched to 5.5 Update 3b, i could not reconnect to vCenter.
The vCenter was running version 5.5 Update 2.
The solution was to upgrade vCenter to 5.5 Update 3b.
The Release notes for vCenter and ESXi 5.5 Update 3b has been updated to reflect this:
|Note: In your vSphere environment, you need to update vCenter Server to vCenter Server 5.5 Update 3b before updating ESXi to ESXi 5.5 Update 3b. vCenter Server will not be able to manage ESXi 5.5 Update 3b, if you update ESXi before updating vCenter Server to version 5.5 Update 3b|