You see something like the following error in the message logs of the backup job:
CESPIV10-FileIO JobId 62: ASR: GPT partitions detected. GPT partitions are not supported at this time!
This error is related to LiveBMR backups. LiveBMR does not currently support GPT partitions and must be disabled if this error message appears. Cold BMR should still work with systems using GPT partitions.