How to mass update records from a List View
Salesforce has a handy feature where you can edit records at once from a list view.
For the filter criteria, select what would comprise the view and this is the most important part: YOU MUST ADD A FILTER FOR THE RECORD TYPE IF THE OBJECT INCLUDES RECORD TYPES. You can only bulk update from list view if all the results are from the same record type. You must set a filter to insure this. Even if the object has just one record type and it's your default for all records, you must filter for record type in order to edit a list view.