I am having this very same issue and can't seem to get it straight....
  I have gone to start menu, typed cmd then done Cntrl-Shft-Enter to go into admin mode and I type in "C:\Program Files (x86)\Cakewalk\Shared Surfaces\FaderPort.dll"
I hit enter and then get this error:
*this file does not have a program associated with it for performing this action.  Please install a program or, if one is already installed,create an association in the Default Programs control panel.
 
Which I have tried but in the default programs control panel I can't find a damn thing regarding the faderport, nor midi control devices etc.  Any help?! 

It should be noted (though it doesn't seem to matter as the issue is the same as it was in X2.....) that I am running X3 producer (just installed it), and that the faderport works like a champ in Studio one.