Not something I have seen reported but the fairly quick solution would be to uninstall Rh11 and make sure the PDF add-on is uninstalled as well, then reinstall without the add-on. I believe that should work but if in doubt, you would have to ask Adobe direct. Installation questions are free.
See www.grainge.org for RoboHelp and Authoring tips
If you have installed Rh 11 and then installing Acrobat XI Pro, there should be no concerns as such. This doesn't seem to be known i think.
Could you please attach screen shot of the error message or if you can share the error log ?
It turns out that it was the PDF add-on that was causing the problem. My IT department removed it and then tried pushing the Adobe Acrobat install through, and it worked. Strange...