I have updated my system early to Ubuntu 9.10 (Karmic Koala) and, to my surprise, there is a little change that could cause dramatic problems in Zlib (library dealing with compressed data). The gzopen() function has been changed to gzopen64(). This means that all calls to gzopen() in the PHP bindings for that library should probably be modified to use gzopen64().
In Dokeos, we use PclZip 2.6, which doesn’t use gzopen(), apart from a check to see if the zlib extension is installed or not. I have reported the problem to PHPConcept (the guys in charge of the PclZip development) to report the problem. Meanwhile, if you are using PclZip in your PHP app and it needs to run with a recent version of zlib (I have zlibc 0.9k-4), you will probably have to edit the PclZip library file and change gzopen() to gzopen64().