The Compact Flash corruption in the secondary partition could cause the upgrade to fail and restore to the old code.
In fwdl.log you will find the below log
Aug 30 21:20:25 fwcmit:SW/1 Repairing the secondary partition now.
Please run bad block test to confirm there is a Compact Flash corruption How to check a VDX for CF Issue using the “badblocks” command
If there is no bad blocks found please contact GTAC.