Sounds like your jobs are mostly configured to use "WAN" optimization instead of "Local". You can't mix jobs with two different optimizations into the same Backup Copy. However, if you've somehow already run a backup copy and the interval expired or otherwise ended (perhaps by triggering a "force sync") I've seen cases where the Backup Copy transfers nothing at all, but creates the metadata file assuming 1M blocks so future runs will fail with this message.
It should be possible to recover from this situation by disabling the Backup Copy job, going to the Backups and right clicking and selecting "Delete from disk" to delete any backups associated with that backup copy job, but be sure to also check the "Remove archived backups" option. Note that this will DELETE all information from the disk associated with that Backup Copy job so only do this if you know there is nothing in the Backup Copy you want to keep.
Just reenable the copy job and don't interrupt it until it starts copying data (don't do a force sync or anything like that). If data won't start copying on the first pass without selecting "force sync" then you need to understand why as selecting force sync will likely cause the error to reoccur.