Access2007 graph on report prob with reference to form

I don't use microsoft graph that often but am using it in Access2007 and
have the graph based on a query.

Works fine if when the where clause of the query is
WHERE (Year([InventoryMonth]) = 2009)

However doesn't work in I change the query to be
WHERE (Year([InventoryMonth]) = Forms!frmReport!ComboYear).

Note the form is open and the ComboYear control has the value 2009.

The query runs fine and displays same data but the graph will not display
any data.

I can construct the query in code but just wondered if there is a
workaround?

Thanks in advance,
Mark