Thanks to JaRC for the super important code he placed here:
and in all likelyhood you wil find an item named "Disable Performance Counters" in the right hand pane, set it to 0 and everything should be right as rain the next time you boot.
This message from several years ago proved invaluable to me just now. I had tried Process Tamer briefly in the past, but yesterday I decided to use it again. To my dismay, I couldn't get it to run. Same story as so many other messages in this thread, but I wasn't using any of the programs mentioned. However, when I came upon JesusInsideMe's message, I went into RegEdit and gave it a try. Bingo! All is now well.
I now realize why PT had worked when I tried it earlier but hadn't this time until I made the registry change. A week or so ago I tried JV16PowerTools' settings to speed up my computer. Sure enough, one of them had to do with disabling performance counters. None of what I did made much difference in my computer's speed, and I simply forgot about it. But I'm almost certain that that was what blocked PT from running.
Anyway, many thanks to JarC and JesusInsideMe (who called my attention to JarC's message).