HP Photosmart 2575 wont print in IE7 Protected Mode

I have an HP Photosmart 2575 All-in-one printer. It has been printing pages
from IE7 with no problems for a couple of months, using the drivers built
into Vista Home Premium 32bit. Sometime between about 27th April and 5th May
it stopped doing so. Now the print icons appear in the IE7 Statusbar, and
then in the System Tray but the printer queue is empty and the printer is
not classified as active. If I turn off Protected Mode, printing works fine.
Everything is patched up to date regularly.

I have rolled the system back as far as I can, deleted and re-installed the
printer, installed the new (latest) full-featured software from the HP
website all without any improvement. This printer does not use the HP
Director software but the newer replacement, HP Solution Centre. In any case
I have the most up
to date Vista specific version from the HP website dated March 2007.

Anyone else getting this? How come it suddenly broke? Have any of the recent
patches or upgrades done anything in a relevant area?

Reposting in the hope of some more help :-)

Hugh