Yep Ithis is touching on the problem I already know they have to be the same name. There are 32 bit versions of PCL 5 & PCL6, but the 64bit driver page only lists the Universal Printer Driver. Humph!
I've been trying to use the 64-bit Printer driver using my PC and the 64-bit Win install DVD as sources but can't find the right files.
In the end I just gave up and used the Universal Printer Driver for both 32 & 64. Not had any problems with it so far, so perhaps HP have actually made them more reliable (they were updated in Jun 2010).
Cheers
John
