Windows 10 Need Assistance Updating

The error is because of the dual boot. The installer is confused on where to install. Is your dual boot on separate disks or one? If you have multiple disks, remove the 8.1 disk and try again.

As neemo says, if your dual-boot is on a single hard drive, you're going to have a problem. In that case you'll need to MAKE CERTAIN YOU HAVE ALL YOUR PERSONAL DATA (LIBRARY FOLDERS) BACKED UP TO EXTERNAL MEDIA FROM BOTH W8.1 AND W10 PARTITIONS FIRST BEFORE PROCEEDING!!

If you are doing a Clean Install using the MCT tool with the AU update (post Aug. 2nd), it will completely erase your hard drive and all partitions on it. Thus the backup caution above. I would recommend that you purchase a separate hard drive for the W8.1 and install the W10 on your 1st original hard drive. Then use Recovery Media (DVD or USB) if you have them to install your factory W8.1 on the new HDD. You can then use W10 BCD menu to accommodate dual booting, or Partition Magic, or Grub Disk to boot to either Windows version on either disk upon startup.

Another alternative I use in my W10 test machine where I have 2-W10 hard drives and 1-W7 hard drive installed is I use my computer's BIOS (Dell Dimension E520) to let me select which hard drive I want to boot to. When my computer turns on, I can use the <F12> key to change the boot order preference, and select whichever of my 3 hard drives I want to run and the corresponding Windows version therein. This allows me to have all 3 hard drives physically cabled to SATA ports on my Motherboard, and I never have to open the case to change Windows version. It's extremely convenient as I support many of my Customers on both W7 & W10, as well as being an Insider Tester for Microsoft on W10 new releases. This may work for you if you have a desktop PC or self-built PC. If you have a laptop, you'll have a more difficult time.

Unfortunately, I don't have a legit W8/8.1 license, so I am unable to test the dual boot with W10 AU version (v1607 b14393.105). If you are in the laptop category, you might have to consider running the W8.1 on top of the W10 once you get it installed on your C:_bootdrive using virtual-ware such as VMware or Hyper-V or similar. This might be worth trying. One of our other Techs here might have done this, and can add some input into the conversation and let you know if this is possible with the newest W10 update version. As MS comes out with them every month now, it's difficult to keep up with all the possible OS configurations, such as the 600 versions of Linux out there that people are dual-booting with W10 or multi-booting with.

Hope this information provides some choices for you.
Best of luck to you,
<<<BIGBEARJEDI>>>

It appears that it has to do with the dual boot on the same disk I'm trying to update. Even though it seems Windows updates are working, the build number remains the same.

Perhaps we didn't make it clear, the latest update of W10, the AU (Anniversary Update) WILL NOT AUTOMATICALLY INSTALL THROUGH WINDOWS UPDATE!!! You must use the Microsoft MCT tool and do a CLEAN INSTALL of W10, which wipes out all programs, settings, and data from that hard drive! So you must be certain to backup all your personal data to external media first or suffer possible irretrievable data loss!

This is a know bug with the W10 AU, and you can search this forum for ANNIVERSARY UPDATE to read about the details in 3 or 4 threads we have going about it. Also, Yes, we have reported it to Microsoft on several occasions, and they have no ETA on fixing it for us. Sorry!

<<<BBJ>>>