If you are trying to boot to a Windows Installer via UEFI, then you will need to use a FAT partition to hold the boot files because UEFI will only boot from a FAT partition (the EFI boot partition on a GPT disk is formatted as FAT).
The easiest thing to do, is to simply convert the whole ISO to a FAT32 partition image by dragging-and-dropping the ISO file onto the MPI_FAT32 Desktop shortcut to make a .imgPTN file.
The resultant .imgPTN file should then be UEFI-bootable and MBR-bootable (though for Win7 x64 UEFI booting, you need to tweak the files a bit - see here for details).
The best (most compatible) way to UEFI-boot is to have a USB drive containing a single FAT32 partition. However, the maximum file size for FAT32 is 4GB.
The solution is to split the Install.wim or Install.esd file into smaller files.
The new Split_WinISO.exe Windows utility will do this for you. Just feed it the ISO and it will make a .imgPTN file for you (or a new ISO with split WIM files).
The easiest thing to do, is to simply convert the whole ISO to a FAT32 partition image by dragging-and-dropping the ISO file onto the MPI_FAT32 Desktop shortcut to make a .imgPTN file.
The resultant .imgPTN file should then be UEFI-bootable and MBR-bootable (though for Win7 x64 UEFI booting, you need to tweak the files a bit - see here for details).
Large Install.wim or Install.esd files
The problem comes when you meet a Windows Installer ISO that contains a file that is over 4GB in size (for instance \Sources\Install.wim or \Sources\Install.esd). If you try to make a FAT32 .imgPTN file using MakePartImage, it will fail when it tries to copy the very large file to the FAT32 volume!The best (most compatible) way to UEFI-boot is to have a USB drive containing a single FAT32 partition. However, the maximum file size for FAT32 is 4GB.
The solution is to split the Install.wim or Install.esd file into smaller files.
The new Split_WinISO.exe Windows utility will do this for you. Just feed it the ISO and it will make a .imgPTN file for you (or a new ISO with split WIM files).