Thanks for the feedback, but it didn't work. Flash Player is enabled on my web browser, and ActiveX Filtering is disabled. But I still keep getting prompted to install Flash Player when I visit sites like nbcnews.com.
You've probably got cached files that keep sending outdated info to pages you visit.
Download this file: Deep Clean.zip
Close IE. Check your task manager to be sure the iexplore.exe process is terminated.
Unzip the file.
Double click the deepclean_set.bat file.
A command prompt window will open and your Disk Cleanup settings manager will open too.
Check EVERY box in the list and click OK.
Then double click the deepclean_run.bat file.
Again, a comman prompt window will open, and your Disk Cleanup will run, clearing many more files than the standard cleanup does. It WILL take a while to cleanup.
When it finishes, you can delete the deepclean_set.bat file as you won't need it again, but keep the deepclean_run.bat as it can be used to "deep clean" your disk whenever you need it. Save it in your documents folder.
Afterward, open IE again and go back to NBC. You shouldn't see any prompt to upgrade anymore.