This is going to depend on a lot of factors related to how you operated and the circumstances under which you sold the business. I would advise that you speak to a local business attorney and get into detail with him or her.
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This requires a very fact-specific analysis of a large number of different factors, including whether corporate formalities were observed. You should consult with a California corporate attorney as soon as possible.
The general trend in recent caselaw is that the corporate veil will only be pierced if it's demonstrated that the corporation was the instrumentality of fraud or other improper conduct. If the facts you relate are true and complete, I think it's very unlikely that a court would pierce the veil.
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