the size of the pclinux 2011.9 kde iso is 647 mbs
if you downloaded it form another place than this linkhttp://distrib-coffee.ipsl.jussieu.fr/pub/linux/pclinuxos/live-cd/pclinuxos-kde-2011.09.iso
it could be a broken file or that the file you downloaded is not complete
sometimes a incomplete file works partially but when you install it you discover problems on it
I downloaded from the link provided
http://distrib-coffee.ipsl.jussieu.fr/pub/linux/pclinuxos/live-cd/pclinuxos-kde-2011.09.isoThe same link you listed....the link on the PCLinuxOS KDE page. Check sum matches.
The file size of the iso is 647.2 megs as reported in dolphin.
When it burns to disc, K3b reports that 584 megs completed and the disc was succesfully created.