Adding "all" to combo box isn't working

so I have two combo boxes in a form and I need to be able to look up data 
with either one or both, meaning i need one to have an "all" option (or
just 
be null).  I tried putting this in the rowsource: 

SELECT DISTINCT [SNM Data].[SNM Type] FROM [SNM Data] UNION Select Null as

AllChoice, "(All)" as Bogus From [SNM Data]
ORDER BY [SNM Data].[SNM Type];

and it gave me an error message that says: "The number of columns in the
two 
selected tables or queries of a union query do not match."

I also tried changing the criteria for the field that is being filtered in

the query to this:

Forms!NameOfForm!NameOfCombo Or (Forms!NameOfForm!NameOfCombo = "any")
 
Another problem I'm having is that I have a command button that is
supposed 
to use the values selected in the combo box to filter data from the table 
into a subform (basically filtering and locating records) I am using the 
below code, and for some reason if I exit the form and pull it back up the

button stops working unless I first right click the form, select "Filter
by 
form" and then "apply filter/sort"  I want other people at my work to just
be 
able to pull this up and find what they need via the combo boxes, so I
really 
need it to work automatically.

Option Compare Database
Option Explicit



Private Sub Command44_Click()
    Dim strWhere As String                  'The criteria string.
    Dim lngLen As Long
    
    If Not IsNull(Me.Combo22) Then
         strWhere = strWhere & "([SNM TYPE] = """ & Me.Combo22 & """) AND
"
     End If
  

    If Not IsNull(Me.Combo24) Then
            strWhere = strWhere & "([ICA] = """ & Me.Combo24 & """) AND "
        End If
        
    lngLen = Len(strWhere) - 5
    If lngLen <= 0 Then
        MsgBox "No criteria", vbInformation, "Nothing to do."
    Else
        strWhere = Left$(strWhere, lngLen)
    Debug.Print strWhere


    Me.Filter = strWhere
    Me.FilterOn = True
    End If
End Sub