Help mij met Error Message 5 in VB6

[Tjipie]

Hi, ik ben een beginnend VB6-programmeur en schrijf een appl. om mijn boeken te beheren. Daarin houd ik in een tabel ook de uitgevers bij.

Met de API call Sendmessage zoek ik vervolgens naar een bepaalde publisher. In de ontwikkelomgeving werkt het prima maar in het .EXE bestand krijg ik de volgende foutmelding: Error message 5 - Invalid procedure call or argument. Hoe kan ik dit oplossen. Hieronder is (een deel van) de code:

Public Declare Function sendMessageByString Lib "user32" _
   Alias "SendMessageA" (ByVal hwnd As Long, _
   ByVal wMsg As Long, ByVal wParam As Long, _
   ByVal lParam As String) As Long

Public Const LB_SELECTSTRING = &H18C

Case cmdFind    '-- Find a specific record
            
            Dim iReturn As Integer
            gFindString = ""
            
            With frmFind
                .addCaption = "Type Publishers Name to find"
                .recordSource = "SELECT Name FROM Publishers ORDER BY Name"
                .Show vbModal
            End With
            
            If (Len(gFindString) > 0) Then
                
                With Data1.Recordset
                    .FindFirst "Name = '" & gFindString & "' "
                    If (.NoMatch) Then
                        iReturn = MsgBox("Publisher Name " & gFindString & _
                                    " was not found.", vbCritical, "Publishers")
                    Else
                        iReturn = MsgBox("Publisher Name " & gFindString & _
                                    " was retrieved.", vbInformation, "Publishers")
                    End If
                End With
            End If
Private Sub List1_DblClick()
    
    'get the item the user clicks on and assign it
    If (InStr(List1, "'")) Then
        gFindString = SrchReplace(List1)
    Else
        gFindString = List1
    End If
    Unload frmFind
    
End Sub

Private Sub txtFind_Change()
    
    Dim entryNum As Long
    Dim txtToFind As String
    
    txtToFind = txtFind.Text
    
    entryNum = sendMessageByString(List1.hwnd, _
                LB_SELECTSTRING, 0, txtToFind)
    
End Sub

Private Function SrchReplace(ByVal sStringToFix As String) As String

    Dim iPosition As Integer        'where is the offending char?
    Dim sCharToReplace As String    'which char do we want to replace?
    Dim sReplaceWith As String      'what should it be replaced with?
    Dim sTempString As String       'build the correct returned string
    
    sCharToReplace = "'"
    sReplaceWith = "''"
    iPosition = InStr(sStringToFix, sCharToReplace)
    
    Do While iPosition <> 0
        sTempString = ""
        sTempString = sTempString & Left$(sStringToFix, iPosition - 1)
        sTempString = sTempString & sReplaceWith
        sTempString = sTempString & _
        Mid$(sStringToFix, iPosition + 1, Len(sStringToFix))
        iPosition = InStr(iPosition + 2, sStringToFix, sCharToReplace)
    Loop
    SrchReplace = sTempString

End Function

Alvast bedankt
Tjipie