In my previous post, I was mistaken when I said that MC25 does not experience the same problem. It does, but only when I switch back and forth between running the different versions.
Let's say I ran MC26 yesterday and shut down my computer when I was done. The next day, if I run MC25, I get the UAC prompt asking me if the program can make changes to my system. If I select Yes, it makes the necessary change and starts up with no problem. Then, if I shut down MC25 and start MC26, I don't get UAC prompt and I just get the error. The only way to get out of this funk is to right click MC26 and select run as administrator. Once I do that, it works properly until I run MC25 again.
I suspect that this problem will continue until I remove MC25 from the system. For now I have changed the pinned shortcut to MC26. If it works properly for me for the next few weeks, I will remove MC25 from the system, thereby eliminating the possibility of that error from happening again.
While that may have fixed it, it is not a good idea to run a program as an administrator. Generally speaking it is not secure.
I too have the same problem with the 64 bit version.
After installing Media Center 26, the program started up correctly. I shut it down, then ran MC 25 just to make sure that it was working properly. I then shut that down, and started MC 26 again. That is when I got the Unable to Register Controls error.
MC25 does not seem to have a requirement to run as an administrator