Okay, to everyone who's got the issue of this error message: "The installation source for this product is not available. Verify that the source exists and that you can access it."
This is what worked for me to re-install my Adobe 8 Standard and get updates all the way through Ver. 8.1.6. (I think you should forget about finding the "Source" because I think that is really a red herring and you'll end up spending way more time screwing around compared to simply following these steps.) Also, while the following steps are time consuming, I just don't believe that there is any other way to fix whatever when wrong with any thing in Adobe Acrobat. Consequently, the process does take time, but it works completely.
First, you have to get the Windows Installer Cleanup Utility at this site: http://support.microsoft.com/kb/290301. Then download the Installer Cleanup Utility and run it. You should get a window which lists all of the programs for which the Windows Installer can be removed. DON'T REMOVE ANY PROGRAM LISTED EXCEPT ADOBE ACROBAT 8 OR YOUR VERSION OF ADOBE ACROBAT. (Also, make sure you have temporarily disabled your antivirus and anti-spam,anti-spyware, etc. programs.)
Second, you will not be able to use Add/Remove programs for Adobe 8 but that didn't matter for me because now that you've useed the Windows Installer Cleanup Utility for Adobe 8, you should be able to install Adobe 8 completely fresh or new just as you did the first time. For me, I just ran my Adobe 8 CD on one PC and ran my other Adobe 8 program download on my other PC (I bought two programs of Adobe 8) and after the programs installed new or fresh, I then proceeded with getting all updates through Ver. 8.1.6. Everything worked just beautifully.
You should note that the Windows Installer Cleanup Utility apparently makes it possible to reinstall a previously installed program because it apparently removes certain program components that would otherwise indicate that the program is already installed. In short, the Utility removes whatever software items are used to keep you from re-installing. Also, when you run the Utility, it effectively renders the Add/Remove Programs function useless for your Adobe program because it no longer recognizes the Adobe program as being installed.
Finally, while I did not need to upgrade to Adobe 9, I believe that if you are having the same error message when you are trying to uninstall Adobe 8 to install Adobe 9, the above-stated process will work just as well for you and you should then be able to make a clean install of your Adobe 9 program.
If you go through the above-stated process and you're successful, please post to the forum so others know that it is certifiably correct. If you go through it and it does not work for you, please post your comments about what went wrong or what did not work, making sure that all of us know which version of Adobe Acrobat you were working with.
Good luck!!
