Nelson,
That means you have "corrupt" C6 and C9.1 environments. Perhaps you just copy and pasted C6 and C9.1 from one machine to another or a "registry clean" (optimizer) tool damaged your C6 and C9.x registry entries? Because the C6 and C9.x environments are not correctly registered with Windows, Clarion auto-detection does not work.
BTW, you need the "Vista fix" for the old C6 on UAC-aware operating systems. But it's also possible this 3rd-party vendor does not support C6 any longer and that's why auto-detection does not show C6 as an installation option.
http://www.lindersoft.com/forums/showthread.php?t=18582
Friedrich