The Lego Digital Designer (LDD) software automatically updates itself every time you open it. Somewhere around v 3.0 Lego changed the definitions of some of the bricks and beams in the model, particularly the defined error tolerances. As a result, if you ask the new version of LDD to open the models on the STEM and STEM2 CDs, which were created with an earlier version, you will get a message that some number of the bricks in the model weren’t loaded.

We have rebuilt the models to version 4.3.6 and posted the new models in the “Free Software” section of our web site at:
https://www.vernier.com/downloads/#free

The updated versions should open and generate build instructions without any problem. The models look and function identically to those described in the STEM and STEM2 books.