My Windows 8.1 PC did the automatic update which included the "ACER ADB
Interface update for Windows 8.1" drivers. This happened while I was away
and this afternoon when I came home I was asked to re-boot the PC to enable
updates to be applied.
Since the updates were applied I have not been able to connect my Nexus
7 (2012) as a "MTP USB Device". I have spent hours trying to find a
solution including doing a factory re-set on the tablet.
The tablet connected successfully before I went away! That was a clue.
So I did a Windows Restore to an earlier restore point. What do you know?
The Nexus 7 now connected just like it did before.
I then checked for Windows Updates but carefully looked at what was
being updated. The ACER ADB update was listed as an "additional update". I
have marked it to be forgotten and then applied the other updates. So far
So after all that; try restoring your system to an earlier restore point
and select not to install the ACER ADB update.