Hello,
I have been to this site a couple of times in an attempt to find a resolution to this issue. Lots of times techies give long winded answers and or links to articles to appear as 'brainacs' or to put us through some work because they had to do some digging. But I like to get to the point. I am still using Win 7 (32 bit).
- Turn the Microsoft Arc mouse bottom up ( on the other side away from infamous scroll strip)
- At the very end of the mouse (the end farthest from the battery compartment), remove the plastic piece.
- That's all.
- Afterwards you may want to fine the mouse so that it is working the way that best suits you. That is Start Menu -> All Programs -> Microsoft Mouse and Keyboard Center