Other than knowing that you are using the FREE PRIME Version of Studio One 3, there is not enough information here to be able to give a clear and precise answer to your question.
- What interface are you using?
- PRIME does have some limitations, are you rendering the tracks first or just trying to playback after a take or two?
- more information about your setup is needed.
We also suggest that you take a look at the Studio One 3 Manual: