Thanks for you reply.
No, there is nothing unusual about the hardware running this Windows 7 installation. There is only one NIC. The workstation is a Dell Optiplex 790.
I've just tried to uninstall and (re)install the Ghost Client pointing to another Ghost server (the previous one installed on a laptop that we used before (same version 11.5.1.2266)), and it's working, the workstation appears in the Ghost Console...
It's very strange...
I suppose that I could focus my researchs on the Ghost console of the "new" server, but I don't want to break it. 160 computers (XP OS) are registered in, and it must stay "available" until students are here!
If you have any suggestion, it'll be great!
Thanks.