Per the error message, the main thing that was missing on the autocode command was the argument procs_only=1.
This assumes that your model is made up of "Procedure" superblock hiearachies and thus creates a set of callable procedures. I'm not presently running with version 7 here, so I can't comment on the particular template that you are using, but I would assume that in contains the correct "wrapper" for a callable User Code block to link into your MatrixX simulation. We have, however, successfully used the approach that you are attempting to create to allow for accelerated simulation of larger models. The main disadvantage with this approach is the the loss of access to the details within each of the "autocoded" models.