I spent many hours trying to get flash 10 to install. I used all the help and tips Adobe offered to fix the problem to no avail. The I ran 2 different Registry utilities to clean up my registry and then manually went throught the registry removing and keys that mentioned ADOBE, SHOCKWAVR or Flash. I also went through the files and folders on my hard drive removing everything that mentioned ADOBE and still I received the same error. Looking under the covers there appeared to be a problem registering the Flashplayer files.
Next I searched the internet and got more tips about Registry folders to change permissions on and or delete and I did that and still got the error. From all of this I did learn that there was Flash version 8 at one time on my computer as I could see it mentioned in the registry and the previous owner may not have removed it all. I suspect this was the problem.
Anyway someone on the internet pointed me to the log file that is left behind a failed install and that still showed a failed to register issue. I can see the install process creating files but not able to register them. That pointed back to something still holding things up in the registry.
So I simply went and ran regedt32 and instead of trying to find a bad key that was the problem I went to HKEY_CLASSES_ROOT and changed permissions on that high level key to full control to the current user name (me). You have to know how to change permission and I started out not knowing how to do it but figured it out. You may get a message that it could not change all the permissions but it seemed to change enough of them to provide access for the Flash 10 installer to register the flash 10 files.
I then reran the installer for flash10 and it ran to completion! EUREKA!