Hello,
I just had the same problem with my Zenbook UX303LB.
Solved it as follows (I just translated this, hope you find what I mean):
# Start Devicemanager (Windows Key + R, devmgmt.msc, run)
# Searched for the Device with the 'problem sign'
# Right Click and Update Driver
# Search manually
# Choose from a list of drivers
# Select USB MassStorage Device
# Next
Solved it for my system, hope it will help you as well! :)
Cheers!