I was expericing the same problem as Joachim. However, it was happening for me in version 3.6.7-2 and it was telling me the error was on line 1828.
I was able to solve this problem, though. I manually downloaded 3.6.2-2 and installed it. Then I re-ran ddclient. It complained about not having the right cache file format, but it worked. Then I apt-get upgraded to 3.6.7-2. I re-ran ddclient, and it again complained about the cache format, but the error message went away. Now it appears to be working completely as expected. Seems like an odd fix, but it seems to have worked. FYI. -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]