What's the build-id?

So I’m trying to deploy a custom wim for windows 7 and I keep running into a weird error: Error: Unable to find SETUP , needed to install the image

This is what I managed to find and it works really well.

http://www.pburch.com/blog/2010/03/05/a-tale-of-build-numbers-and-deployment/

A Tale of Build Numbers and Deployment

March 5th, 2010 Posted in MDTMicrosoftWDSWindows 7Work

I’d just like you to know that I’ve been pulling my hair out all week.  I’m practically bald now.  We’ve been using MDT 2010 for quite some time and I’ve been super happy with it.  Until this week.
So, I’ve been creating custom images this week and capturing them to my MDT machine.  I got around to the x86 image, customized it, updated it, captured it, imported it, then tested and failed.  I couldn’t figure out why – hence the hair pulling.  And then I found it.  Like a glowing pot of gold hidden under a rock in the deepest part of the forest, I found the problem:
The DVD I got the source files from in the top image was build number 6.1.7600.16385.  Some update that I was running on the image I was customizing was updating this build to 6.1.7600.16481.  So, when I would go back to try to test the customized image, I’d get an error at the start of the task sequence that goes something like this:
Operating System deployment did not complete successfully. Error: Unable to find SETUP , needed to install the image MDT_ServerDeploymentShare$Operating SystemsW7×86_CAP_3-4-10W7×86_CAP_3-4-10.WIM I tried the Google route, and found a bunch of unrelated stuff.  Turns out, if the build number is the same on a custom image as on an image with the full source files, MDT will not require setup sources for the custom image.  It will take it from the existing sources in another OS.  So, when it was looking for the setup sources for my 16481 build, it couldn’t find it.
There you have it.  Be careful running updates on custom images.  Make sure you have the sources with the same build number or it won’t work.