With document ID c03689762 on 2013/03/08 an advisory for HP Data Protector 6.20 (6.21) and 7.0 (7.01) was released, describing a problem when running an incremental backup of a virtual machine using the virtuel environment integration and with change block tracking activated after a previous incremental backup failed.
As a workaround a new full backup is recommended until a fix becomes available.
The complete advisory can be read here: http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=c03689762&jumpid=em_alerts_us-us_Mar13_xbu_all_all_2028506_143185_software_critical_005_38