Verify 25600 bytes of flash with checksum.
Verify successful
done in 0.036 seconds
SAM-BA operation failed
CPU reset.
An error occurred while uploading the sketch
Win 7 x64 pro here and not seeing that error with IDE 1.8.5
I do have all the Arduino program locations in my security's exclusions list though.
Am also using USB 2.0 ports only via a powered USB 2.0 hub.
Will try another IDE to be sure.
EDIT
Not seeing it with 1.8.6
Not seen on CREATE
Not seen on 1.9.0 BETA
Given that I am on the same OS I suspect a local issue of some kind.
What that is I am not sure.
Could you try a test by turning off any additional security and using a USB 2.0 port.
Not sure if it will help but it will rule out a couple of common issues.