I have spent most of today trying to get my N12 working with Windows 7 Ultimate 64 bit, (retail, purchased a few days ago, full version) having "in place" upgraded from Vista Ultimate 64 bit.
Kept getting "cannot initialize" (or something similar) trying to open the Yamaha Steinberg FW Driver control panel, which I thought had installed successfully but had not (the same Vista 64 drivers I installed with Vista) also could not see the device in My Computer Device manager.
Googling and reading posts in various forums led me on a trail to Steinberg.Net where I downloaded TOOLS FOR MR 64 bit version 1.5, and with the n12 powered off, I ran 'setup' in the "Driver_" folder.
This seemed to take a long time (more than a few minutes) to complete, but when it had done so I found 'Yamaha Steinberg FW Bus' in 'sound, video and game controllers' in device manager, and the Steinberg FW Driver control panel now opened up and showed as normal.
Then I powered the n12 on, and observed 'Yamaha Steinberg WDM Audio' and 'Yamaha Steinberg WDM midi' appear a few moments later under 'sound, video and game controllers' in Device Manager.
I checked sound files played back OK then started Cubase 5 (64bit) and noted that the 'Cubase' light on the n12 did not come on, and the transport controls did not work so I then went into my original (Vista) 'wintools_for_n_v200x64' folder and from the 'Extensions_' folder I ran 'setup'.
Then starting Cubase 5 again, the 'Cubase' light came on, and the transport controls work OK.
I appreciate this may not be a stable interim solution but I am more hopefull now of my n12 running in Windows 7 64 bit, as it seems to be working using the MR816 driver.
I will report back again after I get finished with reinstalling some VI's
but in the meantime,...
Brian