Lookup fields problem....

Help please...

I can't get the 'Lookup' field option to work in Delphi 2 when using more than 1 field to lookup the result field. The lookup field properties are:

object Table1GroupName: TStringField
  FieldName = 'GroupName'
  Lookup = True
  LookupDataSet = Table2
  LookupKeyFields = 'GroupType;GroupNumber'
  LookupResultField = 'GroupName'
  KeyFields = 'GroupType;GroupNumber'
  Size = 30

When I run the form, the 'GroupName' field is displayed, but if I attempt to change it I get the following error message:

        Field 'GroupType;GroupNumber' not found.

Pressing OK simply redisplays the error message again!

It looks like the field names aren't being parsed correctly, but I can't think of a work-around!