I have exactly the same problem with MS Explorer. Using Vista 64 bit and a new computer.
I am also having the same issue with XP and Explorer, Chrome and Firefox. None of them will open a .pdf any more. I have full version of Acrobat 9 and also ver 8 of reader installed and neither work. I get the same error message.
HI Dave! I got this problem, I'm not sure it's what you got too: I cant open PDF on websites but i can opn PDF files in my copmputer, once it's downloaded. When I tried to instal version 9, it wont finish instalation and it says "make sure you have access..." it also says something about HKEY\MACHINE\SOFTWARE...MSFS. Any idea how i can fix it?
from my experience, the administrator forgot to grant access right to me when they upgraded my adobe reader.
I have to request them to regrant the right and reboot the machine, and it work fine.
Hope this may help you.