[AccessD] Problem with combo box audit

I receive an error when I add acCombo Box to the If conditions: 

If .ControlType = acTextBox Or .ControlType = acOptionGroup Or .ControlType
= acComboBox Then       	If .Value <> .OldValue Then

Help says the following:

"Operation is not supported for this type of object. (Error 3251) 

You were attempting to execute a method or assign a value to a property that
is usually valid for the object, but is not supported in this specific
instance. For example, the Edit method is generally valid for Recordset
objects, but not for a snapshot-type Recordset. This error could also occur
in cases where the operation is not permitted due to the type or status of
the object - as when trying to use the MovePrevious method on a
forward-only-type Recordset. Some operations are also not supported,
depending on if you are accessing a Microsoft Access database engine or an
ODBC data source."

I have no clue why a combo box can't support Value or OldValue -- anyone run
into this before? I'm stumped. If I remove the check for a combo, it works
fine everytime. I'm running this from the form's BeforeUpdate event. 

Susan H.