Enterprise Administration > About Purging > Limitations and Conflicts in Purge > Delete Conflicts Not Supported by Purge
  
Delete Conflicts Not Supported by Purge
The following conflicts may appear when items are deleted, but do not occur during a purge job. This is because you cannot delete the latest iteration of an item or the master iteration.
Cannot delete documents associated with parts
Cannot delete a WTPart used by another WTPart
Cannot delete a WTDocument used by another WTDocument
Cannot delete a CAD document used by another CAD document
Cannot delete a CAD document referenced by another CAD document
Object is Associated to a Change Issue (Problem Report), Change Request (ECR), or Change Activity (ECN task)