It’s not a must, but Google recommends you use the latest fastboot and ADB file from the latest Android SDK available, to install a factory image on your Nexus device, and that apply to Marshmallow factory images too.
We’re not sure whether this would solve the problem some of you are facing while installing the factory image. The said error is error: cannot load ‘system.img’ and we hope it can be solved by manually flashing the system.img and other files using the latest fastboot and adb files we have provided below.
→ Download Fastboot and ADB file package | File: latest-fastboot-adb-files-oct-8-2015.zip (614 KB)
Although old, we’d still recommend you to use quick ADB and fastboot installer here.
To update quick installer’s old files with new ones, do this.
First, simply download the above file, latest-fastboot-adb-files-oct-8-2015.zip.
Extract it into a separate folder to get 4 files from it.
Now copy these 4 files, and paste them into a folder named ADB in C drive of your PC. Click Yes, when it asks to replace files. (This folder was created by quick installer, and had old files.)
That’s it. You now have latest fastboot and adb files with proper drivers and all, and accessible system-wide.