I wish someone would answer this! I have same system and same problem with YouTube. Did not have before "up"grade.
Try going here:
Follow the link for the uninstall instructions. I'm not sure how to best tell what your last version was exactly. If you have kept up on updating, then the last version was 11.6.602.171. It would be in the list of versions at the bottom of the page.
You can also look at the Flash install log in C:\windows\system32\macromed\flash and see what version was installed prior to the one you have now.
After several installs, uninstalls, and reinstalls I finally got version 11.6.602.171 working. I think my Norton was interferring with install, but still took me two tries after turning Norton off.
I had 10.3 xxxx for a long time and just click on automatic upload. Have turned that off.
Thanks for you help.