Having difficulty downgrading my Nexus S 4g My Sprint Nexus S 4g is running CyanogenMod 9 (ICS 4.0.4).

I want to use stock 2.3.6 which I got from https://sites.google.com/site/baroqueworksdevandroid/offcail-binary. In recovery mode I get this error:

assert failed: getprop("ro.product.device") == "crespo" || getprop("ro.build.product") == "crespo"

Error

Status 7

Installation aborted`


Now I realize at this point that this has SOMETHING to do with the variety of cryptic code names for the Nexus S phones as well as a possibility that the current ROM I am using might have the wrong code name embedded in it, making my downgrading difficult.

1) What is the code name for the Sprint Nexus S 4g which is a CDMA phone but not the Verizon codename?

2) Does that link have the proper ROMs for this phone?

3) Other options? I need to flash this back to 2.3.6
1) What is the code name for the Sprint Nexus S 4g which is a CDMA
  phone but not a the Verizon codename?


The crespo codename is the GSM variant of the Nexus S (Verizon never carried it). Sprint's NS4G is simply codenamed crespo4g.


  2) Does that link have the proper ROMs for this phone?


No, those are all for the GSM crespo version.


  3) Other options? I need to flash this back to 2.3.6


Where can I find stock or custom ROMs for my Android device? covers your options pretty well. In this case, the first heading of the answer will be a good start:


  Google Flagship Updates
  
  Google hosts update packages for the flagship Nexus devices at
  http://android.clients.google.com/packages/. You can't browse that
  link directly, but web search is your friend here. Search for that
  link plus the code name of the device and the version you want; for
  example, searching android.clients.google.com/packages crespo ics
  results in a lot of pages with this link -- the OTA Ice Cream Sandwich
  update for the T-Mobile Nexus S.


Searching for android.clients.google.com/packages "crespo4g"  gingerbread returns a number of results. One of them is this XDA thread, with a collection of links to stock firmwares.