SPQuery Update SPListItem

Hi,

I have a SPQuery with some ViewFields and ViewFieldsOnly = True. I'm getting the items from a list with this query and some of the field values I'm trying to update. The fields that I would like to update are from the ViewFields. But I'm getting the error"Value does not fall within the expected range." On the forums I found that SharePoint needs some more fields in the ViewFields in order to be able to update the items. But which are those fields? 

Thx.