The most common solution is always to try a fresh set of AA alkalines and don't forget to put your controller into bootloader mode
And be sure not to hold down the right thumbstick or the green A button during detection and programming.
Before you get too far down the road of trying to 'fix' your Windows 7, you might see if you can find a buddy with a Windows PC you can borrow - if the Viking controller works on another PC, then the problem can be narrowed down to your PC. There's always the possibility that one of the wires in the controller got 'knocked loose' some time from the first time you programmed your controller until now.
I would think back and try to remember if you've installed any new devices recently. I thought Windows 7 was pretty good O/S, but I had a lot of troubles helping Vista customers back when I was selling "KeyGrabbers" - one time a guy installed his PalmPilot and it screwed up the drivers for the KeyGrabber (who would have guessed).
The ol' google search for Windows 7 Code 43, I was surprised at the sheer number of hits of people with Code 43 problems. Some people suggested taking a BIOS upgrade, others suggested trying to plug in or unplug combinations of other devices seemed to help.