A payment in excess of what the participant or beneficiary is entitled to receive is an overpayment under EPCRS. Rev. Proc. 2008-50 has correction methods for overpayments. Of course, you will have to determine which program you are under; SCP, VCP, etc. The easiest way to find information is to search the Rev-Proc for "overpayment".
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Rev. Proc. 2008-50, Section 5.01(3)(c) Overpayment. The term “Overpayment” means a Qualification Failure due to a payment being made to a participant or beneficiary that exceeds the amount payable to the participant or beneficiary under the terms of the plan or that exceeds a limitation provided in the Code or regulations. Overpayments include both payments from a defined benefit plan and payments from a defined contribution plan (either not made from the participant's or beneficiary's account under the plan or not permitted to be paid either under the terms of the plan or under the Code or regulations). However, an Overpayment does not include a payment that is made pursuant to a correction method provided under this revenue procedure for a different Qualification Failure. Overpayments must be corrected in accordance with section 6.06(3).
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Rev. Proc. 2008-50, Section 6.06(3) Correction of Overpayment failures. An Overpayment from a defined benefit plan is corrected in accordance with the rules in section 2.04(1) of Appendix B. An Overpayment from a defined contribution plan is corrected in accordance with the Return of Overpayment method set forth in this paragraph. Under this method, the employer takes reasonable steps to have the Overpayment, plus appropriate interest from the date of the distribution to the date of the repayment, returned by the participant or beneficiary to the plan. To the extent the amount returned to a defined contribution plan is less than the Overpayment adjusted for earnings at the plan's earnings rate, then the employer or another person must contribute the difference to the plan. The Overpayment, adjusted for earnings at the plan's earnings rate to the date of the repayment, is to be placed in an unallocated account, as described in section 6.06(2), to be used to reduce employer contributions (other than elective deferrals) in the current year and succeeding year(s) (or if the amount would have been allocated to other eligible employees who were in the plan for the year of the failure if the failure had not occurred, then that amount is reallocated to the other eligible employees in accordance with the plan's allocation formula). In addition, the employer must notify the employee that the Overpayment was not eligible for favorable tax treatment accorded to distributions from Qualified Plans (and, specifically, was not eligible for tax-free rollover).