Windows 8 HTC One Sync Manager No Phone Connected

Problem

After installing HTC Sync Manager on Windows 8 or 8.1 in order to manage your shiny new HTC One (m8) as I did, Sync Manager may show "no phone connected" despite the phone showing up in Windows Explorer.

Solution

Navigate to the C:\Program Files (x86)\HTC\HTC Driver\Driver Files\Win8_x64 directory, right click on androidusb.INF, and choose "Install". You may need to reboot but in my case HTC Sync Manager started working right away.