Unable to restore stock OS on Nexus S I had a post on https://android.stackexchange.com/questions/14999/how-can-i-restore-the-default-os-on-phone-that-has-custom-build
however this got closed because it was a possible duplicate. Unfortunately the duplicate did not answer my question so I am posting again with further details.

Basically I had built the Android source and flashed this to my phone and now I would like to go back to the stock version. 

The link in the duplicate points to the following recovery file http://android.clients.google.com/packages/ota/google_crespo/f182cf141e6a.signed-soju-ota-102588.f182cf14.zip

I renamed this to update.zip, and reboot into recovery. I then get a triangle with an exclamation mark. Then I hit the power and volume up key again and see more options, so I then selected 'apply update from /sdcard'. 

I receive the error: 

 E:failed to verify whole-file signature 
 E:signature verification failed 
 Installation aborted 


How can I restore my phone with stock Gingerbread?
It's an official update, so the signature should be perfectly valid.  There are a couple things to check:


You didn't mention where you saved the update.zip.  Make sure it's in the /sdcard/ folder -- try viewing it via a file manager on your phone to ensure it's there.
I assume you've done this already, but make sure your bootloader is unlocked.
The download might have been corrupted.  Try the download again, and verify its validity with the MD5 sum (3e8908941043951da5a34bb2043dd1a0)
What's your specific model number?  Perhaps this update doesn't work for your model.

You can try this 2.3.6 for the GT-i9023 / GT-i9020t: http://android.clients.google.com/packages/ota/google_crespo/1ada25375426.signed-soju-ota-189904.1ada2537.zip
Or this 2.3.6 for the GT-i9020a: http://android.clients.google.com/packages/ota/google_crespoa/0b9c8148de0d.signed-sojua-ota-189904.0b9c8148.zip