The problem can be observed if the .cnf or .xml configuration file of the IP phone is corrupt or missing from the Program Files\cisco\tftpPath directory. This error can also be observed if the Cisco CallManager Domain Name System (DNS) name is used instead of the IP address in the System > Server configuration.
To address this issue, verify the contents of XMLDefault.cnf file to determine that the phone's configuration file is appropriate.
Also, perform these steps:
In the Cisco CallManager, Go to Service > Service Parameters . Select CCM IP address and Cisco TFTP service.
Click on Advanced and set File Delete to True. Make sure that File Location is actually the TFTP path, and click on Update. Restart the TFTP service.
Delete and re-add an IP phone that is having the problem. Stop and restart the TFTP service again.
Sometimes changing the Cisco CallManager Domain Name System (DNS) name (host name) to the IP address under System > Server configuration helps. Also, go to the URL directories (Select System > Enterprise parameters > Phone URL Parameters section > URL directories), and change the portion of the URL that has the Cisco CallManager host name to its IP address.