Windows 7, I just got the HTC One M9 and run into this same problem. I had the M7 and M8 previously - I still have them. The M8 syncs fine. I've never had an issue. M9 simply will not be recognized by the Sync software on any of 3 computers (all windows 7, one 32 bit two 64 bit). The computer recognizes them and I can navigate into the storage etc. I've done all I can think of, uninstall reinstall reboot restart etc etc. I tried deleting the driver and the HTC Driver app thinking maybe the M8 driver was a conflict but no help. I did the process recommended on this thread with AndroidHTCSync.apk, that file is on my phone however it will not run. It says "Parse Error". And the file size is 0.00kb so I wonder if its corrupted? So called smart phone. Open to new ideas, even to download a new version of AndroidHTCSync.apk file if I can find it from a reliable source.
I have noticed a few things with the M9 that are buggy, particularly bluetooth issues.Times out a lot syncing to new devices but once synced it stays. However, you can't make 2 phone calls. After the first call I can hear them but they cannot hear me. And why does it ask me which device I want to sync to every time I make a call (M8 did that too)? Distracting, and annoying, and its pretty obvious if I wanted to dump the connection I would do it before dialing. Too bad, I have been an HTC fan but wonder what's going on in Taipei, Taiwan. I dig their philosophy of not trying to reinvent every 2 years but the basic stuff has to run seamlessly.