Steam an error occurred while updating disk write error
Much to my dismay, Fallout 4 in Steam was displaying a DISK WRITE ERROR. I verified the Fallout 4 files, and then scanned my hard drive for errors, as recommended by Steam. In the end, I solved the problem by going into Program Files (x86)/Steam/steamapps/common and there was a file down the bottom titled Fallout that was 0KB in size.
If changing the download region didn’t work, we can check your existing firewalls to see if they are disabling steam to write on the hard drive.
There is no need to resort to this solution if a simpler one works for you.