If there's a problem with the backup database, usually the Repair button in the console will correct the error. Read the topic "Tell me more about repairing the backup database" in the console help for more information, including some warnings.
In this case you may have a disk problem which has not yet risen above the threshold for Windows Home Server to warn you, so you may need to
run chkdsk on all the drives in your server, followed by another database repair.
I'm not on the WHS team, I just post a lot. :)