Have you followed the troubleshooting steps outlined here:
section: Phones not located with SMNPv3
http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cer/10_0_1/english/administration/guide/CER0_BK_CA66317A_00_cisco-emergency-responder-administration-10_0/CER0_BK_CA66317A_00_cisco-emergency-responder-administration-10_0_chapter_01100.pdf
Have you tried rebooting CER server, on several occasions after spending significant time with similar issues rebooting the server cleared it for me.