Hi Jim,
I would recommend to make sure that the blocks you specify to be tuned (and all their parent models all the way to the top model) are referenced in normal mode (no accelerator mode). The reason is that accelerated mode model references are monolithic entities, effectively like a single S-function, where we are unable to extract tunable blocks inside them for analysis and tuning.
Please let me know if you have any other questions.
Thanks, Erman