I found out that you have to put your phone in Mass Storage mode, since the default is MTP mode. So simple @#! And I spent hours trying all kinds of message reading.
Settings / Xperia / USB Connectivity / USB Connection Mode and select MASS Storage rather than MTP. I unchecked Install PC Companion. It works right away. No need to update drivers, no need to change android_winusb.inf. You may need to kill adb.exe before reconnecting adb devices.
It was for me :)
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