I've searched for this error and read the replies. None of them helped.
I'm running PS CS5 Extended, version 12.0.4. It was just moved onto a new computer. Other Adobe products include Acrobat XI Pro and Reader XI.
After the software was installed on the new computer, I updated Acrobat and Reader with no problems. When I updated PS, IIRC, some updates installed properly, but Extension Manager CS5 5.0 will not install.
I tried manually installing AEM CS5 5.0. It installed without error, but PS doesn't seem to recognize it.
This problem was not happening on my old computer.
I spent more time reading the related posts on this topic and found a work-around, which was to set the clock on the PC back. The post I found mentioned October 2011, so I used October 1, 2011. That worked. PS updated completely with no errors.