Hyper-v cannot boot Gen2 guest from Windows 2012 R2 or Windows 8.1 x64 ISO - file format not supported, Gen1 works fine

Question

I am new to Gen2 Hyper-V and so far I simply can't use it, because I am unable to install any (supported) guest OS from an ISO ...
So far I tried that on:
1. my HP Z230/i4770 workstation (Secure Boot disabled) host running Windows 8.1 Pro x64 (with Hyper-V feature enabled), can't boot any VM with supported OS ISO.
2. my home desktop/i3770K (secure Boot enabled) host running Windows 8.1 Pro x64, same result, error during VM boot from ISO, quoted below.
Synthetic SCSI controller (instance blah blah) Failed to Power on with Error 'The version does not support this version of file format'
Gen1 guests of course work perfectly fine with those ISOs, because emulated DVD IDE picks up the official Enterprise Evaluation ISO of either Windows Server 2012 R2 or Windows 8.1 x64 Enterprise, perfectly fine and all works OK in Legacy boot mode.
When I create a new guest and select Gen2, then no matter if I check or uncheck the Secure Boot in virtual Boot Order options for the guest (while setting the SCSI DVD at top of course), it simply doesn't work, always same error. I tried first connecting
to VM to see if it prompts for key press, but it doesn't, the error is instant on Power on when (supported) ISO image is selected to be booted.
I verified that both of official Enterprise Evaluation ISO's of either WS2012r2 and W8.1x64 are bootable in both the UEFI mode (Secure Boot enabled) and Legacy BIOS mode using a physical computer.
What am I missing here???

Answer 1

FYI, above is wrong! it's not about linking ISO to virtual DVD or selecting "Install OS later", it's all about the location of the ISO file and share permissions on parent folder!
I was actually suspecting several issues, but haven't had time to test it, was thinking about issues like assigning (or not) some of initial settings during Gen2 VM creation, e.g.:
-Network connection through virtual switch or Not Connected (make no different if assigned or not)
-Memory above 4096MB (makes no difference if < or > 4096MB)
-ISO file location (makes huge difference!)
The ISO file CANNOT be placed on network share OR in shared folder on same local drive as the VHDX file (works fine if parent folder is not shared).
I can now replicate the issue easily every time and it always fails with file format unsupported message whenever I have the ISO file located either on remote network share, or (fails the same way too) when I have the ISO file placed locally (on host drive)
when simply a parent folder is shared... must be some permissions issue... and a pretty dumb one considering that in production environments nearly everything is placed on remote file servers ...
... so the moral of the story is, if you want to install Gen2 VM in win8/2012 hyper-V then you must copy the ISO file to Hyper-V host drive AND make sure the parent folder is not shared. works every time now! :)