After Upgrade, Can't Login on Linux Platform: “Backend Host Unresolvable”

On the Linux operating system, after upgrading to Calendar Server 6.3, there are error messages in the http.log file after running start-cal:

cshttpd[2984]: General Error: caldb: 
caldb_pvt_isLocalUrl: hostname of hostname.xyz.com is not resolvable.  
Please check that hostname is correct and that hostname resolver is correct.

Also, after attempting to log in, the following error message is given:

Backend Host Unresolvable
Please try again

Fix: This problem is fixed in Calendar Server 6.3 Update 1, patch number 121658-17.

This is the same as problem number 6516438 in the following section:Reported Problems in Calendar Server 6.3 .