FORM - Cascading Combo Boxes from a linked list in SharePoint

[jerelp]

I've never used a linked list in sharepoint and I've never created cascading combox boxes. I don't know if it is possible to make a SQL statement from the linked list if so how do you do it?

Linked list name is Systems Activity

I need to create combo box that drills down to another combo box

First combobox - Category
Second Combobox - SubCat

I've made the Category combobox bound control source to [Category] and a Row source with a value list:
Development
Out of Office
Support

the SubCat combobox the control source is unbound and the row source is also unbound which gets it source from VBA

if it were to drill down it would be
Out of Office:
sick
vacation
leave
personal
Development:
project
database

The code in vba is:

Private Sub Category_AfterUpdate()

Dim filter As String

filter = Category.Value

SubCat.RowSource = "Select [Systems Activity].[SubCat] From [Systems Activity] WHERE [Systems Activity].[Category] = " & filter & " Order By [Systems Activity].[SubCat];"

SubCat.Requery

End Sub

When I do use this i get a
Syntax Error(missing operator) in query expression '[Systems Activity].[Category] = Development'.

'Development' is the value in category combobox


PLEASE HELP!!!!!!!