Word 2000 mailmerge document has had two merge fields added to accommodate
two new columns in Excel data source. Invalid Merge Field error refers to one
of the new fields 'This merge field is used in the main document, but it does
not exist in the data source.'

Well it does!

The data is in custdata.xls in sheet1 in a named range 'custdata'

Any ideas why additional fields not being picked up?