is just one backupset which causes this error?
Are there any processes rsync, backup, .. which accesses this file?
Where is the backup set located (network mount, local, usb, raid, ...)?

I happens for every backup set.
There were no processes that accessed the backup files.
The backup file was on a local hard disk.

If I rename my "jobs" directory and create a new empty jobs directory, the backup succeeds. It doesn't like my jobs directory.

One clue: My jobs directory is on a second partition via a symbolic link:
/Users/Shared/Jenkins/Home/jobs -> /Volumes/Jenkins/jobs

changed to new feature, because the usecase is to link parts of the home directory

thank you chris,
this is the problem, it will not support links.

can you explain my why you have the job configuration out of the home directory?

We were trying to get around an unfortunate flaw in the design of Jenkins - the "jobs" directory contains both inputs (config.xml) and outputs (the "builds" directory). Some of our builds can get quite large, so we moved the entire "jobs" directory to a separate partition where we could manage it better. We then regularly back up the config.xml files onto the primary partition.