Please check the error message that you're receiving very carefully. I suspect that you have mistyped something. It is very hard to research an error message if we don't know exactly what it says.
Also, Symantec makes a "removal" tool that I would recommend that you run. The last 3 Symantec (Norton) installations that I have worked on all required the manual removal tool in order to properly be uninstalled.
They make the tool for a variety of their utility programs, so take special note of the name and version number.
What I suggest is this; use the uninstaller on the 2006 version. Once that is removed and the computer restarted, use the manual uninstaller for the 2003 version. Once that has been run, and the system restarted, reinstall the 2006 version.
Norton Uninstall At the link, locate the exact product (the 2003 version you mentioned). Go to the knowledge base and search for "Removal Tools". What you're looking for is program removal, not virus removal.
The tool will be something like this one:
Removing Norton AntiVirus 2003 AIf you cannot find the tool, you can post here again, providing as much information about the program and the make/model of your computer system, including the Operating System.
Since you've already purchased your AntiVirus software, I'm sure that you don't want to hear this, but in the spirit of "helping" I must comment. I do not recommend any version of Norton AntiVirus or Internet Security to anyone. I believe that their software is not very good and seems to cause more problems than it solves. If you're interested, there a couple of "free" antivirus programs that have earned my trust. One is AVG by Grisoft and is available by download. Find the link on my Home page at
http://www.dwightblackburn.com/As I write this, the Grisoft download site is not working. You can attempt to get to the page through this page.
If you don't have a good firewall, the ZoneAlarm is a good one.
Vansrme (Chris) recommends another set of products, which you can read about on this AP page:
Click HereDwight