Printer HP c7280: No Installed HP Devices Found

[Gerard Robin <g.robin3@free.fr>]

Hello,
When I configured my printer HP c7280 (Photosmart all-in-one) the
command: sudo hp-toolbox got me:

No Installed HP Devices Found
To install a device, use one of the following methods:
---------------------8<------------------------

ERROR: No device found or unsupported device

However with http://localhost:631/admin/ in my browser I configured my
printer and now I can print with all my programs: lpr, vim, openoffice
...
For example lpq gives: 

Photosmart_C7200 is ready
no entries

Why sudo  hp-toolbox failed ?

tia
--
Gérard