Grub2 installation failed when trying to install Ubuntu Zesty Alpha

[the_mechanical]

Tried to install Ubuntu Zesty Alpha (DVD-Image on USB-disk, created under Ubuntu 15.10 with Startup-Disk creator [or how it is named] ).
Configuration:
AMD64, Started USB-Installation in UEFI-Mode
Disk 1 - SSD (Win7 only, has it's own boot manager there)
Disk 2 - SSD (one new partition for Zesty, one existing for Wiley, GPT Partition table)
Target for Grub was Disk 2 (/deb/sdb)
Disk 3 - HDD

At the moment I'm switching between the systems with chosing the boot-hard-disk at boot. So starting win I chosse Disk 1, starting Linux is Disk 2.
At the end I want to boot Grub from Disk 2 with an entry to Win7 - but for the first i need a running Zesty ;-)

BIOS:
Secure boot is off
Fast boot is off

Can't tell you if it was possible at the end, at the moment I'm still in Installation-Mode, Firefox opened after sending the bug.
Will try to solve it before reboot.

For Information - I'm not a linux-expert, "only" an advanced user (little terminal knowledge, able to compile easy stuff from source *gg*)

ProblemType: Bug
DistroRelease: Ubuntu 17.04
Package: ubiquity 17.04.7
ProcVersionSignature: Ubuntu 4.9.0-15.16-lowlatency 4.9.5
Uname: Linux 4.9.0-15-lowlatency x86_64
ApportVersion: 2.20.4-0ubuntu2
Architecture: amd64
CasperVersion: 1.380
Date: Wed Feb 22 11:01:32 2017
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntustudio.seed boot=casper only-ubiquity quiet splash --- cdrom-detect/try-usb=true noprompt persistent
LiveMediaBuild: Ubuntu-Studio 17.04 "Zesty Zapus" - Alpha amd64 (20170219)
ProcEnviron:
 LANGUAGE=de_DE.UTF-8
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 LC_NUMERIC=C.UTF-8
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)