Cannot back up

I cannot backup my macbook pro. I keep getting a backup failed message everytime I try.

Using Time machine buddy this is what I got:

Starting standard backup

Backing up to: /Volumes/Seagate Slim Drive/Backups.backupdb

Event store UUIDs don't match for volume: Macintosh HD

Node requires deep traversal:/ reason:must scan subdirs|new event db|

Node requires deep traversal:/Users/Maria/Pictures/iPhoto Library/Database/apdb reason:contains changes|must scan subdirs|found in deep scan|missed reservation|

No pre-backup thinning needed: 20.41 GB requested (including padding), 187.24 GB available

Indexing a file failed. Returned 200 for: /[>, /Volumes/Seagate Slim Drive/Backups.backupdb/Macintosh/2015-03-29-170601.inProgress/AA6A77FB-A091-4B4 9-92E7-3E0EDB43D62F/Macintosh HD/[>

Aborting backup because indexing a file failed.

Stopping backup.

Copied 1 files (24 KB) from volume Macintosh HD.

Copy stage failed with error:11

Backup failed with error: 11

Any help?

Thanks!