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I disagree in concept with the other answers, but as a practical matter, it is unlikely you could prevail.
Liability for the negligent administration of employee health plan benefits is an issue governed by a federal statute known as ERISA. ERISA makes it virtually impossible to get damages for poor administration of a health care plan. You can usually only get the policy benefit you should have received if you prove that the conduct of the plan administrator was not just wrong, but an abuse of discretion.
Depending on the nature of the "mistake" and the benefits lost, you may or may not have an ERISA claim. However, damages other than the policy benefit are not available to you. If the amount in controversy is large enough, you might be able to get an ERISA attorney to assist you.
You should locate and consult with an ERISA law attorney as soon as possible to explore your facts and determine your options. I would suggest you look either on this site in the Find a Lawyer section, or go to www.cela.org, the home page for the California Employment Lawyers Association, an organization whose members are dedicated to the representation of employees against their employers.
Good luck to you.
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