Maybe try running TuneECU in compatibility mode?
To do this:
1. right-click the TuneECU shortcut or exe file
2. click "Properties" in the right-click menu (bottom)
3. select the "Compatibility" tab
4. check the "Run this program in compatibility mode for:" box
5 ...and try "Windows XP" fromt he drop-down menu.
Try this and let us know. I am also running Window 7 64-bit, but with no problems. I didn't need to run TuneECU in compatibility mode, but it's worth a try.