I had this error and kept trying to reinstall thinking that my options were wrong. I eventually checked the bug list and found that it is a known thing.
https://bst.cloudapps.cisco.com/bugsearch/bug/CSCux57704
The work around is to "Correct the host system date and time, then reinstall APIC-EM".
This happens during the configuration wizard and you have to input an NTP server which gets validated (or so it says after clicking Next) so I'm not sure how you would do this in the middle of the install. Has anyone else found a way around this bug?
