vba adodb parameter query fails

I have the following issue with an adodb parameter query that fails with an error or returns an empty recordset. However a similar DAO query succeeds.

This is all in MS Access

First the SQL - Find_Post_Code - This is designed to take either or both parameters:

PARAMETERS [Local] Text ( 255 ), FState Text ( 255 );
SELECT PCodes.postcode, PCodes.locality, PCodes.state, PCodes.long, PCodes.lat
FROM PCodes
WHERE (((PCodes.locality) Like "*" & [Local] & "*") AND ((PCodes.state)=[FState])) OR (((PCodes.locality) Like "*" & [Local] & "*") AND ((([PCodes].[state]) Like [FState]) Is Null))
ORDER BY PCodes.locality;

Now the ADODB Function:

Public Function GetPostCode(varLocality As Variant, varState As Variant) As String
'//Purpose: Return Post Code for a varLocality and/or varState

  Dim cmd As New ADODB.Command
  Dim rst As New ADODB.Recordset

On Error GoTo Handle_err

  With cmd
    .CommandText = "Find_Post_Code"
    .CommandType = adCmdStoredProc
    Set .ActiveConnection = CurrentProject.Connection
    .Parameters.Append .CreateParameter("Local", adVarChar, adParamInput, , CStr(Nz(varLocality, "")))
    .Parameters.Append .CreateParameter("FState", adVarChar, adParamInput, , CStr(Nz(varState, "")))
    rst.CursorType = adOpenStatic
    Set rst = .Execute
  End With

  If Not rst.EOF Then
    GetPostCode = rst!postcode
  End If
  rst.Close

Handle_err:
  If Err Then
    MsgBox "Error " & Format(Err.Number) & " " & Err.Description, vbCritical, AppTitle
    Err.Clear
  End If

  Set rst = Nothing
  Set cmd = Nothing

End Function

This fails with the error message: Error 3708 Parameter object is improperly defined. Inconsistent or incomplete information was provided.

If I cast the parameter as adBSTR there is no error, but the resultant recordset has no data

However, If I use the following DAO function all is well

Public Function GetPostCode2(Locality As String, State As String) As String
'//Purpose: Return Post Code for a varLocality and/or varState

  Dim db As Database
  Dim qd As DAO.QueryDef
  Dim prmLocality As DAO.Parameter
  Dim prmFSTate As DAO.Parameter
  Dim rst As DAO.Recordset

On Error GoTo Handle_err

  Set db = CurrentDb
  Set qd = db.QueryDefs("Find_Post_Code")
  Set prmLocality = qd.Parameters!Local
  prmLocality.Value = Locality

  Set prmFSTate = qd.Parameters!FState
  prmFSTate.Value = State

  Set rst = qd.OpenRecordset

  If Not rst.EOF Then
    GetPostCode2 = rst!postcode
  End If

  rst.Close

Handle_err:
  If Err Then
    MsgBox "Error " & Format(Err.Number) & " " & Err.Description, vbCritical, AppTitle
    Err.Clear
  End If
  Set rst = Nothing
  Set prmLocality = Nothing
  Set prmFSTate = Nothing
  Set qd = Nothing
  Set db = Nothing

End Function

I would prefer not to swap and change between ADODB and DAO to accomplish my aims. Your help would be greatly appreciated