Just enter the CS3 serial number when prompted for an eligible product.
You'll find all your serial numbers, if you registered, in your account at Adobe.com under the Adobe ID used to register them.
I downloaded the CS6 version but when I enter my serial number (from my account at Adobe.com), it says that there is no eligible product on my PC... so my serial number is not for CS6... but I guess for the initial CS3 version I had bought... before doing an upgrade to CS6 years later...
So, back to my key question... if I download CS3 from Adobe and use my serial number... I guess that will work, but how do I get back my upgraded CS6 version?
No. CS3 had its own serial number and that’s what you need to verify you’re eligibility for the CS6 upgrade.
I think you misunderstand. The upgrade installer is looking for a previous version of ID which is eligible for the upgrade, so you need to find the s/n for CS3 and feed it to the CS6 installer after it tells you it can't find an eligible product. You wouldn't get that far if the serial number you provided in the first step was wrong.
OK, here is the situation:
* I am an Adobe customer
* I bought in 2008 CSInDesign CS3 and I have the serial n° [removed by moderator] in my Adobe account (shows as Adobe InDesign, version = CS3, platform = Win)
* In 2012, I upgraded my CS3 to CS6 and I have a serial n° [removed by moderator] for that in my Adobe account (shows as Adobe InDesign, version = 8.0, platform = Win)
After my PC crash, I downloaded InDesign CS6 and use my serial n° of 2012. It doesn't work, as it says my product is not eligible.
So, here is where I stand now...
* I downloaded CS3 and used my serial n° for InDesign CS3. It works. I now have CS3 on my PC
* How do I get back my 'upgrade from CS3 to CS6?
* I have the serial number for that upgrage and I guess I need to download an "upgrade" file somewhere from Adobe. But I cannot find it, I found pages with upgrades, but there are so many different files, I do not have a clue which one to use;
This is now my key question... can someone give me the link to access the file(s) I have to download to upgrade my InDesign CS3 version to InDesign CS6
I think maybe you should contact customer service directly and see if they can get you either a replacement upgrade installer or a replacement serial number. We can't do those things on the forum.