A broken attribute entry is when the attributes for a file (read only, archive, system file ect...) are not found.
Generally not bad as it will be given new attributes and sent on it's way.
There are no hard and fast rules about why this happens, the mechanics of a hard disc are very sensitive and how they store so much data in such a small place is amazing, but unfortunatally anything from a slight knock to cosmic ray from space can affect the data on the disc.
The only thing you can do is to keep backups of your data and programs so if something really bad happens it won't be too painful to get your pc up to speed again.