What needs of the other party are not being met? 
If you reach a deadlock the best suggestion is to STOP discussing the CONTENT and review the PROCESS of the negotiation. Perhaps the first thing to do is change the time and place of the negotiation. A fresh start is often a sure way to get things moving again.
1. Make sure you have summarised the areas of agreement and have a common purpose clearly defined.
2. Review the consequences of a failure to reach an agreement.
3. Take a fresh look at other options. Consider a joint task force to deliver this.
4. What alternatives remain open? Consider trialling one for a period.
5. Find the issue that will bridge the gap between you and the other party.
None of this is easy. Negotiation is hard work but keep remembering what you and the other party needs from the process and you’ll get there.