After upgrading our vCentre server to the latest patch (vCentre 4.1.0-345042), our Update Manager failed to update or even attempt to scan any of our hosts with the error “Host cannot download files from VMware vCenter Update Manager patch store. Check the network connectivity and firewall setup, and check esxupdate logs for details.”
I have searched on the web for the solution to this error and people were mentioning double checking DNS entries on each of the hosts, but that never changed in my case.
I went back to our vCentre server and checked each vCentre server component version installed and it turned out that VUM wasn’t running the latest version. After upgrading and rebooting the machine, ESX host and VM scan and updates were working back again.