You get this error when you configure the /etc/krb5.conf file to use a domain name that you cannot resolve correctly. Its strange becuase often I find that if I do an nslookup of the server name, it works properly. However, if I enter the domain name of kdc server inside /etc/krb5.conf I get this error. Its a relatively easy fix. Just change the domain name into the IP address of your kdc server.
lib/main.php:944: Notice: PageInfo: Cannot find action page
lib/main.php:839: Notice: PageInfo: Unknown action
lib/plugin/WlugLicense.php:99: Warning: Invalid argument supplied for foreach()