Some of the newer images have some different things going on with the indexes (8.1) If you keep experiencing problems with 7z you can try mounting the wim with diskmgmt.msc or manually with dism/imagex
Actually, I'm working with Windows 8.1 ISO's on a Windows 7 x86 machine. Another problem discovered yesterday: only UltraISO 9.6+ can edit Windows 8.1 ISO's without losing UEFI boot sectors. Before that, I was using UltraISO 9.3, now I've migrated to UltraISO 9.61. About 7-zip: I don't know what is the exact error message in English, but translating from my language it's something about this: "Can't open C:\...\...\sources\install.wim as a archive". Here is version is 9.20
Interesting about the Ultraiso thing... I remember trying to save boot sectors and apply them to iso files and they would only seem to work on single layer dvds... It's strange I haven't heard of anyone making a graphical version of oscdimg... that would seem like a really useful thing to have.
I did it! Works from USB and DVD. Support Dual Boot (x86 and x64) for BIOS and UEFI. UEFI x64 xttp://s018.radikal.ru/i527/1403/22/371d9a3fb039.jpg xttp://s52.radikal.ru/i135/1403/22/322de37a79ae.jpg xttp://s018.radikal.ru/i510/1403/da/681ad15e49eb.jpg UEFI x86 xttp://s006.radikal.ru/i214/1403/0b/dfc4feb192e7.jpg xttp://s019.radikal.ru/i616/1403/76/9174bc10f118.jpg xttp://s52.radikal.ru/i137/1403/e4/6bbee06f61fb.jpg BIOS x64/x86 xttp://s52.radikal.ru/i137/1403/9c/878c466ebc44.jpg Note. If PEFirmwareType = 2, PC is booted in UEFI mode.
Must commit i disliked these ESD files first, but the decrease in size is superb. 4,3 GB WIM vs. 3,4 GB ESD is nice on my Easy2Boot Stick and saved me from splitting a WIM for this awfull Secure Boot Feature (would be interested who is responsible for the idea to limit this new feature to FAT32 formatted usb media - HELLO! ). With ADK 17029 it's fast to convert and able to check the indices for correct flags .