Recently i had encountered a firmware upgrade error on CUCM, where upon restart the phone will display a AUTH FAIL error, Despite using the default firmware on the CUCM (under device defaults) 
I chanced upon a document where in it mentioned that Firmware upgrades of a release earlier than 8.3(3) to 8.5(4) or greater you must upgrade firmware to version 8.3(3) up to a load less than or equal to 8.5(2) after this you can upgrade to a later version.
I had initially downloaded the .cop.sgn file from Cisco (cmterm-7911_7906-sccp.8-5-2.cop.sgn) and loaded it on to both CUCM’s. After restarting the phones i kept getting an ‘error’ on the phone display, despite restarting the TFTP service.
Despite the Phone requesting the firmware we had specified:
<loadInformation>cmterm-7911_7906-sccp.8-5-2</loadInformation>
it was not able to download the firmware. confused, i decided to do a factory reset of the phone and this time it completely broke the phone. the phone was stuck on the Cisco logo :S restarting from time to time trying to install the default factory firmware. but failing at each occasion.
now since i made one phone unusable, i decided to try another phone and while retracing my steps, i came to realise that once a .cop file is installed you cannot reverse teh process :S. I did not want to have duplicate firmware on the CUCM, i resorted to download another version of Firmware from teh CCO but this time in in .ZIP format <cmterm-7911_7906-sccp.8-4-4.zip> this time i TFTP’d all the files onto the root of the CUCM and restarted the TFTP Server. I thereafter assigned SCCP11.8-4-4S to a phone and restarted it. it worked a treat
12:53:01 25: Name=SEP0023EBC6C578 Load= SCCP11.8-5-2SR1S Last=Initialized
13:03:45 25: Name=SEP0023EBC6C578 Load= SCCP11.8-5-2SR1S Last=Initialized
15:04:50 25: Name=SEP0023EBC6C578 Load= SCCP11.8-4-4S Last=Initialized
15:07:03 20: Name=SEP0023EBC6C578 Load= SCCP11.8-4-4S Last=Phone-Keypad
16:21:54 20: Name=SEP0023EBC6C578 Load= SCCP11.8-4-4S Last=Phone-Keypad
16:22:36 23: Name=SEP0023EBC6C578 Load= SCCP11.8-4-4S Last=Reset-Restart
Now i have the job of upgrading 300 phone firmwares ….. going to be exciting :p
