Phones are not auto registering - TFTP Timeout

[shakkeerb]

Our CUCM 11.0.1.20000-2 on BE6K-S. Recently we found that phones are not auto registering. While we manually add phones, it is working. 

In phones status messages is showing TFTP timeout. I did packet capture in Call Manager.

Requst to CTL and ITL is reply with

HTTP/1.1 503 Service Unavailable\r\n
[Expert Info (Chat/Sequence): HTTP/1.1 503 Service Unavailable\r\n]
Request Version: HTTP/1.1
Status Code: 503
[Status Code Description: Service Unavailable]
Response Phrase: Service Unavailable

and

 GET /ITLFile.tlv HTTP/1.1 end up with File Not found 404 error

HTTP/1.1 404 Not Found\r\n
[Expert Info (Chat/Sequence): HTTP/1.1 404 Not Found\r\n]
Request Version: HTTP/1.1
Status Code: 404
[Status Code Description: Not Found]
Response Phrase: Not Found

Also I noticed this error message 

Trivial File Transfer Protocol
Opcode: Error Code (5)
[Source File: ITLSEPC80084AAEA51.tlv]
Error code: Disk full or allocation exceeded (3)
Error message: processing allocation exceeded, try again later

I restarted TFTP server but it didnt solve.

What may be the cause of the problem? Is it a bug in 11.0 version? Is there any 11.5 upragede recommendation? 

Thanks in advance for your support

[Chris Deren]

Does the Device Pool assigned to the phone model device default include CUCM node and CUCM Group with auto registration enabled?

[shakkeerb]

Yea, Auto registration enabled. We are using BE6K-S in this site and only a publisher there. Auto registration was working fine and this week only it started to show the trouble.

[Jaime Valencia]

Do you have proxy TFTP configured?

[shakkeerb]

Yea. TFTP is configured and Phone is communicating with TFTP. But the above error messages are returning.

[Jaime Valencia]

Then try to disable proxy TFTP in that cluster and try again.