I'm running ConMan with FAR 1.70 (build 2087) under Vista Business x64. Got it running after a few tries, but not sure which step was really required. Hope this'll work for you too.
It seems to me that running the two involved .exe files individually first allows to run them combined. Let me clarify: first I created a shortcut to far.exe, configured it (size, font, etc), loaded my settings (stored in .reg files), then ran it. From within FAR I ran conman.exe without parameters. Last, I modified the shortcut to launch conman.exe with far.exe as parameter.
Also tried to play with compatibility settings, but none helped.
My current problem with this version of FAR is that whenever I try to use the built-in editor (F4 or F6 from within viewer) FAR crashes. Going to try an x64 alpha now, see if that helps.