You've probably solved your problem, but here it is anyway:
This error also appears when a newer version of the product exists on the machine, so it is highly likely the uninstall was not clean. 10.0 is seeing the old 10.1.1 on install.
I'm experiencing the exact same situation. I haven't unistalled Standard yet, but I'm afraid if I do, the Pro upgrade I purchased won't work.
I can't believe after spending an extra $199 to upgrade to Pro that I'm stuck with no immediate solution.
Well, you are attempting to uninstall the same code version of Acrobat X Standard with Acrobat X Pro. That won't work. You say that you purchased an upgrade from Acrobat X Standard to Acrobat X Pro that doesn't sound right either. If you decided to get Acrobat X Pro after already purchasing Acrobat X Standard the process should have been to get the full DVD media or the full ESD (electronic service download) from Adobe of Acrobat X Pro and then destroy or return the old software along with a very long legal form that says you are doing just that process. That's a procurement issue from both ends I would think. Needless to say the correct way would be to get the full media with the full serial number for Adobe Acrobat X Pro from Adobe. Then uninstall Acrobat X Standard from your user machines and then install the full media of Acrobat X Pro.