impossibile installare grub su /dev/sda (os win 10)

[Giuseppe]

installing ubuntu studio on win 10 appear this error

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: ubiquity 2.21.37 [modified: lib/partman/automatically_partition/question]
ProcVersionSignature: Ubuntu 4.2.0-16.19-lowlatency 4.2.3
Uname: Linux 4.2.0-16-lowlatency x86_64
ApportVersion: 2.19.1-0ubuntu3
Architecture: amd64
CasperVersion: 1.365
Date: Tue Apr 5 22:54:32 2016
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntustudio.seed boot=casper quiet splash ---
LiveMediaBuild: Ubuntu-Studio 15.10 "Wily Werewolf" - Release amd64 (20151021)
ProcEnviron:
 LANGUAGE=it_IT.UTF-8
 PATH=(custom, no user)
 LANG=it_IT.UTF-8
 SHELL=/bin/bash
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)