When Participant A died, her/his beneficiaries were his/her children, B and C, equally. However, the plan paid the full account balance, net of taxes to B. How should the plan correct this situation, especially if B refuses to communicate to plan representatives and refuses to repay one-half of the net amount distributed?

If the employer wants the plan to remain qualified, then the employer would generally restore C's portion of the benefit to the plan and then have it paid out to C. The ability to get the overpayment back from B is a separate issue.

This may require the plan to commence legal action against the recipient.

If the amount is large enough, you may be able to have this addressed as a criminal matter- wrongful receipt or missappropriation of funds.

I worked on on situation where the participant received 2x the amount and would not return the excess after multiple attempts and explanations, Trustee approached the local DA and explained the facts. overpayment of 500,000. DA opened criminal investigation - money returned.