On the phone you're having a problem with, go to Settings and then to the Status messages. Check if when the phone is reset, if you see "ITL Update Failed". If you do you have a mismatch between the signature of the TFTP file which contains the date/time group information and the ITL on the phone so the phone won't accept it's new TFTP file to update that setting. The easy fix for one phone is to go into Settings > Security Configuration > Trust List. Unlock it with **#, and then select more, erase. The phone will reset and download a new ITL from your TFTP that should be able to validate the config file.
