Phones showing REJECTED but available in UCM

I am facing a strange problem in CUCM , 

I have 1 PUB & 2 SUB ,

2 subs are used as TFTP and call processing , call processing is working fine but phone registed to the SUB1 is showing status rejected and the message on the phone is appearing SEPXYA123.xml file not found and TFTP timeout and CTL not found.

Any one have any idea about this issue solution.