Disagreements are a common part of every negotiation. 

Using their  negotiation styles and negotiating techniques both sides of the table  end up seeing things differently and because of that their progress  towards reaching an agreement can grind to a halt. When something like  this happen, one way to address it is to take the time to work with the other side in order to uncover  facts about what is being negotiated. The reason that both sides have  their opinions may be based on partial or incomplete information. 

By working together, it is possible that you may be able to get the negotiations back on track.