In this scenario, the project manager should schedule a quality review meeting to address the sponsor's concerns. Even though the quality acceptance document was signed, which typically indicates formal acceptance of project deliverables, it is important to address any complaints regarding the quality of deliverables to maintain stakeholder satisfaction and to ensure continuous improvement. The meeting would provide an opportunity to discuss the issues raised by the sponsor, review the quality acceptance documentation, and determine if there are any corrective actions or process improvements that can be applied to future phases of the project. This approach aligns with the PMI's emphasis on stakeholder engagement and continuous improvement within project management processes123.
References: The answer is supported by the principles found in the PMI's A Guide to the Project Management Body of Knowledge (PMBOKGuide) and the Professional in Business Analysis Reference Materials provided by PMI45.