What is your operating system & version?
What is your web browser?
[topic moved to Flash Player forum]
thank you Pat Willener for responding, but I stumbled into a solution last night. I have Mac OS Lion and Safari. After much time-wasting I found a way to change several privacy settings in Safari (which I've now forgotten but they were mentioned in Adobe's help section), then uninstalled my old Flash Player. After that, I was able to install the newer version. Whew!