I tried re-loading printerdrake and the related cups stuff.
It made no difference.
I then tried accessing/installing this network printer from the beta 1, beta 2 and final disks of kde4 2010.
I tried it on four different machines.
I got exactly the same results with all of them.
I then tried it from the installed version of kde4 that was in the repositories.
It worked just fine.
I then decided to try with a different HP network printer and got the same results.
One of those printers was close enough to a computer to try connecting it via USB.
Once I installed it via USB, I went back to the HP device manager and found that it would now allow me to install any of the network printers without the error.
So, it appears that if you want to install an HP network printer, you need to install it using the USB connection first before you connect it to the network.
That seems to change some setting somewhere in the system that allows the device manager utility to access the PPD folder.