HTC One (M8) — Issues about files on USB drive HTC ONE M8

Hi, after I have updated my device to Android 6.0 e HTC Sense 7.0, i'm not able to access files on USB drive anymore.
The USB drive has a USB connector and a microUSB one to be plugged with the smartphone. File Manager (native HTC app) can't show me any files, it just says " no file" on "USB drive" section.
But when I connect my USB drive to the HTC in the pull-down menu i can find a message "USB Kingston Unit". Tapping on that, it shows me all the USB files , but i'm not allowed to trasfer files from INTERNAL STORAGE to USB DRIVE. Only the reverse operation is permitted, that is from USB DRIVE to INTERNAL STORAGE. Now i was wondering why file manager can't access files (that happend just with USB drive: files stored in SD card e Internal memory are available)after updating? Can somebody help me?