Hey there did you get this one to work? Having similiar issues but am outa steam too, so just browsin' old threads :-)...
Basically your apache is saying, that it can't find any KDC(your domain controller), so the authentication is failing.
Perhaps, did you try to authenticate using
to check if the kerberos authentication is working? In your case,
kinit -k HTTP/SERVER.EXAMPLE.COM@EXAMPLE.COM
should probably work too... but I think the fqdn name in keytab(SERVER.EXAMPLE.COM) should match the DNS, which is probably lower-case (server.example.com).