Hi Robert,
I finally makes it working. I did read the article, and tried a few things on the printer drivers and after a few hours I gave up
Today I tried my plotter driver using ArcGIS Server Account, it worked! kind of strange though, I am using my own account in the custom print service, the ArcGIS Server Account doesn't work with my print service for unknown reason, but this is another story.
Thank you for reassuring me that the solution will work, and I tried it again, it worked
Simo