Adding observer to address not working

CUCM Version - 10.5.2

Cisco Jtapi version 10.0(1.10000)-2Cisco Jtapi version 10.0(1.10000)-2

OS - Windows 2008 Standard R2 - 64 Bit

Using Cisco Test Tool when we are adding call observer to phones/terminals. Some of them are becoming green but some are still in red state. On analyzing we found that IP phone with range 10.70.x.x are working fine but phone with IP range 10.60.x.x is not working (i.e. observer are not added properly).

What could be the reason? Is there any Ip range or network dependency? What should I check?

Answer: 

Restarting CTI Manager resolved the issue. Now It's running fine for all devices.