Had the same problem, none of these fixes helped.
In eventviewer, found:
Access to C:\Documents and Settings\xxxx\Local Settings\Application Data\Adobe\install_flash_player_ax.exe has been restricted by your Administrator by location with policy rule {929f94c3-b816-49de-871e-e789991f3c0c}
which seemed absurd, until i recalled having used CryptoPrevent. Yes indeed, running cryptoprevent and turning off the first item (protect %appdata% ... ) allowed install of flash player. Rebooting the system was not required.
So, it is necessary to reduce your system protection in order to install the flash player. None of the other dozens of downloaded programs i have installed in the many months since installing cryptoprevent have required this. Adobe?
Just remember to re-run cryptoprevent and turn the protection back on!