A simple google search will do more than enough.
mikrotik ipsec,error unable to get local issuer certificate(20) at depth:0 cert site=https://forum.mikrotik.com
http://forum.mikrotik.com/t/ikev2-vpn-failing-due-to-certificate-check/140292/1
http://forum.mikrotik.com/t/ipsec-unable-to-get-local-issuer-certificate/127920/1