One thing that sometimes happens is that a taxpayer receives a 1099-MISC from a payer located in California, and the California FTB assumes the taxpayer worked in CA. As @DoninGA said, you'll have to call the number on your notice to straighten things out.
If you're not a CA resident, and you earned that money by working entirely outside CA, it is not taxable by CA.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
