You have defined the indicated column as dominant in a verify join. Whenever the operator enters a value in the field, it will be looked up in this column. Such a lookup operation is very quick when an index is present. No index on the column exists at this time. Without one, a lookup might be extremely slow. Unless the field does not allow operator input (in which case you should remove the asterisk) or the table is very small (a few dozen rows at most), you should create an index for this column before you put the form into use.