In order to break vicious cycle of blame, procurement will need to use their negotiation and conflict management skills, adopting a collaborative and integrative approach. Your first action should be to establish the facts that led to the situation where the relationship broke down. Most day-to-day relationship between buying organisations and suppliers do not of course involve procurement staff, so you will need to consult with your business partners internally to establish their point of view of where the issue and sources of conflict are. You should also contact the supplier and get their side of the story - this is particularly to when you have previously identified the supplier as critical or otherwise important to your operations. Ideally you will be able to apply principled negotiation here, separating the people from the issue, focusing on interests and not positions, and then looking for options of mutual benefits.