What version of the plugin are you using?
The 1.2.4 version that ships with Maya 2018 likely won't load newer sbsars, as the engines are old. The 1.4.1 version should have better compatibility with newer sbsars. This is available on our website.
We're about to enter beta for the 2.0.0 release of the plugin, which should be much more stable, and will be available for Maya 2018 and 2019.