Bootcamp operating system missing error after resizing partition I resized my partition to increase my Boot Camp drive few months ago with Disk Utility on Mac. After that I decided to have more space on Boot Camp partition. I resized it again by setting a new size for Macintosh HD but when I reboot my Mac and hold alt key there was no Windows boot drive visible. I googled and followed this discussion: Repairing Boot Camp after creating new partition based on this answer. After rebooting my Mac I saw the Windows boot option but after selecting it I get System Operating Missing.

Here is current situation of my partions and disk:

gpt show: disk0: mediasize=500107862016; sectorsize=512; blocks=976773168
gpt show: disk0: Suspicious MBR at sector 0
gpt show: disk0: Pri GPT at sector 1
gpt show: disk0: Sec GPT at sector 976773167
    start       size  index  contents
        0          1         MBR
        1          1         Pri GPT header
        2         32         Pri GPT table
       34          6        
       40     409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
   409640  850647624      2  GPT part - 48465300-0000-11AA-AA11-00306543ECAC
851057264    1269536      3  GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC
852326800   84899440        
937226240   39546880      4  GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
976773120         15        
976773135         32         Sec GPT table
976773167          1         Sec GPT header
Firstly - Sorry for bringing up an old question - I just spent a year trying to find the answers and only found questions so I figured I'd answer a past one with my solution

Resize Bootcamp partition:


Boot to MacOS and use disk utils to shrink OS X partition leaving unallocated space on hdd


&lt;-- I believe you are at this point based on the empty space starting at 852326800 -->


Boot to GParted and use the copy/resize function to expand the windows partition to the left (this covers your extended space)
Boot back to OS X and use FDisk to mark the Bootcamp partition as bootable (Was partition 4 in my case and looks to be in your case)
Bless a Windows bootable USB before restart (with startup repair avaliable on it)

sudo bless -mount "/Volumes/**mountedusb**/" -legacy -setBoot -nextonly

Boot to windows usb and run startup repair
Restart and you should be good.