Download from
http://distro.ibiblio.org/pub/linux/distributions/pclinuxos/temp/ synaptic-0.57.2-20pclos2009.i586.rpm
Start Konsole (terminal) su to root and go to the folder where synaptic-0.57.2-20pclos2009.i586.rpm is downloaded,
Type then: rpm -Ivh synaptic-0.57.2-20pclos2009.i586.rpm
Also rpm -Uvh synaptic-0.57.2-20pclos2009.i586.rpm is possible.
Guess after installing aptugrade is working
JohnW