NTBOOT.img can be opened using WinImage.
grub2 is actually calling grub4dos and NTBOOT. So all are using grub4dos.
A different version of bootmgr is used in the NTBOOT.img (size 398356 bytes).
but the issue smells a bit like a memory address/map issue...
I don't have Winimage.
Ok, so then when we run grub2 and try to boot a WIM we call again grub4dos, but from the grubfm.iso content.
I rebuilded the USB stick and added (All of them contiguous):
Rebooted on another MBR PC 8 GB RAM, with exactly same results.
Is it possible to upload your .wim files and PM me with their location so I can download and test?
I cannot reproduce any error with my hardware and wim files.
All my WIM files boot fine from internal HDD or my UEFI_MULTI USB stick using Windows bootmanager and adding them to BCD with BootIce.
They also boot fine using AIO Boot from internal HDD or my USB stick using Windows bootmanager.
They also boot fine from E2B USB stick when using grub4dos.
So it seems to me the problem is on another place not in the WIM image files. Anyway I'm uploading the smalest WIM file 7pe_x86_E.wim (237 MB) to let you test it, as you requested and I'll send you a PM when ready.
Note that the grub2 file manager is most useful for UEFI-booting of ISOs, WIMs and VHDs because this is something that is not possible by using grub4dos. Grub4dos does MBR-booting well and is now working very well so there is little need to test grub2 MBR booting.
I'm agree with you there is little need to test grub2 MBR booting when grub4dos does it very fine, but if it is there as an option, it should work fine.
I allready tested on another PC, now I will try another USB device (to exclude possible bad sectors) and report back my findings.