I have done all that the article suggested including using a mac without antivirus or firewall operating. I have changed USB ports, hubs etc. I have the most direct connection possible to my broadband.
The article is useful and tries to be helpful but I am now in the realms of what next. I have successfully updated to iOS 5 on my iPhone 3GS and my daughter has successsfully updated her iPad. I have failed with her computer. All looked good until the final error message that my Ipad could not be restored. The device cannot be found.
My macbook has a very limited amount of software installed with no antivirus or firwall running. It too has failed.
As I said, I am now in discussion with apple about what next.