In reply to Øyvind Hoveid.

1. The best place to ask SAS programming questions is the SAS Support Communities. You can post sample data and the model that you are interested in.
2. By default, the design matrix is singular because it uses the so-called GLM parameterization. If you re-read the article, you will notice that it shows how to use the PARAM=EFFECT option to obtain a nonsingular design matrix. I think this will resolve your issue.