Jim,

It's because you are not inside a form method while the SQL is actually executing. It's the same thing experienced by p-views where the parameter is an object property. For p-views I use code like:

* p-view parm ... somefield = ?lcSomeField
lcSomeField = thisform.txtSomeField.Value
Requery( "theView" )

In the LostFocus() of the cbo1 you can reset the RowSource of cbo2 to use the current value of cbo1

with this.parent.cbo2.RowSource
   .RowSource - ... + this.Value + ...
   .Requery()
endwith

>A simple form presently with only 2 comboboxes.
>
>The second is dependent on the value in the first, so with a RowSourceType of 3 (SQL) I have "...WHERE BINS = ThisForm.FirstCombo.Value ..." in the RowSource's SQL command.
>
>Doing so results in the error message "Thisform can only be used in method" and the question is WHY?