This error-87 can also occur when copying files to a SharePoint server and the file is of a restricted type. For example, a SharePoint server may be configured not to allow .PST files to be copied to it.
If neither of these apply, it is likely caused by hardware errors and/or disk/file errors (corrupt data). Checking if you can copy the same data via Windows (drag & drop, etc), or changing devices (testing with different external USB drives, flash drives, etcetera) can help narrow down the problem.
Unfortunately, it is a Windows error (error #87, as shown), and it is annoyingly 'unspecific'.