Trying to Create an Index Tag using DefineTag function

(Codebase newbie)

I am trying to create an index tag on an existing Fox dbf file:
ICITEM05.DBF.  ICITEM05 .DBF has a current CDX index file associated
to it.

Here's the code, using the DefineTag function:
   tblIcitem.Close;
   tblIcitem.Exclusive := exTrue;
   tblIcitem.Open;
   tblIcitem.DefineTag('ItemTag', 'ITEM', '', False, False);

the valid expression: 'ITEM' is a valid field in the ICITEM05.DBF
file.

What am I doing wrong?

TIA--patrick