What do I say about why I left my last job?

I have an interview next week and I am unsure how to explain why I left my last job as a payroll clerk. I am in Hartford, in case local advice matters. I also do not want to seem like a risk. What do you say?

Thanks for writing this out. I went through something close to it last year, and it settled down once I kept a simple log of every call and form.