It is unlikely that your claim is still actionable: Statute of Limitations rarely exceed 10 years.
You were required in your conversion to list all your assets--including any partnership or ownership in a corporation.
Your partner (ex-partner?) is asserting the doctrine of judicial estoppel: that a party who has sworn to a position in a court proceeding may not be allowed to claim a contrary position in litigation on a related matter.
At the time of filing the bankruptcy your share ownership of the corporation was an asset. The asset was property of your bankruptcy estate. The value of the asset would have factored in to how much you would have been required to pay back creditors. Regardless of the non-disclosure, ownership still rests with the bankruptcy trustee. Yes, there are criminal implications here (bankruptcy fraud). Your bankruptcy discharge is also at risk of being taken away which means you could still owe the creditors that were partially paid in the bankruptcy. You need a lawyer with bankruptcy experience and you need to get one quickly.
This answer in no way creates an attorney-client relationship. The answer is not a complete answer and requires additional facts in order to provide the best options. The submitter accepts the risk of relying on such an incomplete answer and waives any claims of damages for doing so. As stated in the answer the submitter should contact a qualified bankruptcy attorney is discuss these issues further before any action is taken. Any action taken without advise and counsel of a qualified attorney is inadvisable.
Highly doubt you can reopen the bankruptcy. You cannot be a partner in a corporation. You should have reported your shares. If you had a lawsuit against the other shareholder before you filed bankruptcy it had to be listed in the bankruptcy to bring and the statute f limitations has already run.
You should talk to your own attorney there,because the facts that you have put together here do not make much sense.
Disclaimer: This answer does not constitute legal advice. I am admitted in the States of New York, New Jersey and Massachusetts only and make no attempt to opine on matters of law that are not relevant to those three States. This advice is based on general principles of law that may or may not relate to your specific situation. Facts and laws change and these possible changes will affect the advice provided here. Consult an attorney in your locale before you act on any of this advice. You should not rely on this advice alone and nothing in these communications creates an attorney client relationship.
If you owned part of the corporation when you filed the 13, you had to report it. If there was no value to it, then at least there was no harm done. If you owned it after you filed but before you converted, then it was never an asset of the bankruptcy estate.
Creditors who did not get money in the 13 because they were not notified may not be discharged if they should have gotten money. At this late date, those debts are too old anyway.
Mr. Goldstein is a Virginia-licensed attorney only. The information is not, nor is it intended to be, legal advice. You should consult an attorney for individual advice regarding your own situation. Answering this question does not in any way constitute legal representation. Contacting Mitchell Goldstein or the Goldstein Law Group does not constitute legal representation, nor is any information you provide protected by attorney-client privilege until otherwise advised.