Filter subreport from main report

[Rattlesnake]

Hi ,
I have a Report in Access 2003 , . In the report there are 2 fields RecordID and Category_ID.
In this report I also have subreport, which is linked by the RecordID field.
I want to Filter the subreport by the Category_ID field also. I have written this code but it gives me an error

Private Sub Detail_Format(Cancel As Integer, FormatCount As Integer)
Me!rptSubReport.Form.Filter = "Category_ID=" & Me!CategoryID
Me!rptSubReport.Form.FilterOn = True

End Sub

The error I get is "The setting you entered isn't valid for this property"

How can I filter the subreport.


Thanks