Backing up Exchange 2007 IS using 2012

Our 2007 exchange server IS stores are failing to backup

Backup of exchange 2007 fails with final error: 0xe000fedf - A failure occurred reading an object.

This links to

http://www.symantec.com/business/support/index?page=content&id=TECH178015&actp=search&viewlocale=en_US&searchid=1361270421842

The server and drive the exchange db is on has almost 25% free space. (122GB of 700gb free)

The article doesn't help much other than that.

Anyone else had this?

Lee