In els-cas-templates v2.1, the documentation says biblatex + biber is recommended. However, if we try to use biblatex, the compilation fails. This is because the cas-sc and cas-dc use a length variable that is neither defined in biblatex nor in cas-sc/cas-dc. That length variable is bibsep. It is defined by natbib, which is incompatible with biblatex.

The solution is simple. Just define bibsep in our document’s preamble:

\makeatletter