Filtering in MS-ACCES (vba) acts as Parameter query???

Onclick of a button, a VBA code is activated, in which a filter is set (to records where comboBox has "y" value in it). That's all.

What happens in fact is that when clicking the button I get the "Enter Parameter Value" box,which needs to be filled in.
Why???
I only asked to filter, and the filtering is not made.

The code:
*********************
Me.FilterOn = False
Me.Filter = "myform.comboName='Y'" Me.FilterOn = True 'Activates the above filter
*********************

I did the same for another combobox, and have no problems.
In both combo boxes, the row source type is: value list
and the row source has one value: ("Y" in the above case)

Any ideas?
Thanks