After working without apparent problem for a couple of months, Win7 Backup now refuses to back up my Inspiron 15R. It gets about 67% of the way through but then fails with an error code of 0x80070002. 

I've tried to start afresh by removing all previous backups via the Manage Backup Space option, but nothing happens. I've even tried to delete the backup files directly through Windows Explorer, but this doesn't this work either.

Can anyone help with this problem? The laptop is still under warranty but there doesn't seem to be an option for contacting Dell Technical Support about this problem (except via an expensive phone call).

Thanks