I've found a number of posts about this issue, but haven't solved it yet. I've ran Disk Utility, trashed time machine preferences ,trashed the "inProgress" file and restarted… I've even wiped my disk and reformatted. That seemed to work for a while, but now it's back in being stuck "preparing backup" and never progressing.
I'd love to solve it. I'm running backups via USB to an external hard drive and have been for years.
Is Apple abandoning Time Machine?