Backing Up PSE 11 Catague

Does anyone Know why Backing Up PSE Catalogue fails with the message:

"Backup Failure.  Error encountered while writing fields.  c:\Program Data\Adobe\Elements Organiser\Catalog\My Catalog 1.2\catalogue.pse 1 db."

When clicked it displays a large file from the catalogue which should be backed up.   There is no hint why the failure occured. 

Can anyone help?

Graham Cuddeford