First of all I must say, that ddclient works fine with me. I have installed it on several RH linux machines and yet not encountered a problem.
I want to thank John Wingenbach for the nice sniplet of code for postscript execution. I used it to update the ip-address for the safetp daemon ( see http://safetp.cs.berkeley.edu/ ) run by xinetd. In order to get safetp run properly, I had to rewrite the safetp-file in /etc/xinet.d/ and reload xinetd.
Now works nicely and I can ftp with encrypted data.