Runtime Error 5 - Invalid Procedure call or Argument

Hi I am having this error b/w MsgBox step 2 & MsgBox step 3 . Step 2 is displyed and then i am greeted with this error. If i run my program through the VB

the problem doesn't occur but after making exe file if i run it this problem occurs every time. I am using VB 6.0 on windows 2000.kindly advise.......

'############# find a well ################
Case cmdFind
Dim iReturn As Integer
gFindString = ""
With frmFind
.Caption = "Type Well Number to find"
' .recordSource = "SELECT API_Number FROM Wellbore_Data "
.Show vbModal
End With

iMsg = MsgBox("Step4 ", vbCritical, "Well Number")
If (Len(gFindString) > 0) Then
' Data1.UpdateControls
With Data1.Recordset
iMsg = MsgBox("Step5 ", vbCritical, "Well Number")
.FindFirst "API_Number = '" & gFindString & "'"
If (.NoMatch) Then
iReturn = MsgBox("Well Number " & gFindString & " was not found.", vbCritical, "Well Number")
Else
iReturn = MsgBox("Well Number " & gFindString & " was retrieved.", vbInformation, "Well Number")
txtAPI_Number.Text = gFindString
End If
End With
End If
updateButtons

Case cmdDone
Unload Me
End Select
End Sub
'########################### In the form find i have written this code

Private Sub Form_Activate() ' pg 249
List1.Enabled = False
dtaFind.DatabaseName = App.Path & "\ColumbiaGas.mdb"
dtaFind.RecordSource = "SELECT API_Number FROM Wellbore_Data ORDER BY [Well]"
dtaFind.Refresh
If (dtaFind.Recordset.RecordCount > 0) Then
Screen.MousePointer = vbHourglass
dtaFind.Recordset.MoveFirst
While Not dtaFind.Recordset.EOF
List1.AddItem dtaFind.Recordset.Fields(0) & ""
dtaFind.Recordset.MoveNext
Wend
List1.Enabled = True
DoEvents
End If
lblCount = "There are " & dtaFind.Recordset.RecordCount & " Wells"
Screen.MousePointer = vbDefault

End Sub

Private Sub txtFind_Change() 'pg 252
Dim entryNum As Long
Dim txtToFind As String
txtToFind = txtFind.Text
entryNum = sendMessageByString(List1.hwnd, LB_SELECTSTRING, 0, txtToFind)
End Sub
Private Sub List1_DblClick() 'pg 253
' get the item the user clicks and asssign it
iMsg = MsgBox("Step1 ", vbCritical, "Well Number")
gFindString = List1
iMsg = MsgBox("Step2 ", vbCritical, "Well Number") ' ????????????????????????????????????????????
dtaFind.Recordset.Close
frmFind.Hide
Exit Sub
'Unload Me
iMsg = MsgBox("Step3 ", vbCritical, "Well Number")
End Sub
Private Sub cmdCancel_Click() ' pg 254
Unload Me
End Sub
Private Sub Form_Unload(Cancel As Integer)
'Set frmFind = Nothing
Unload Me
End Sub

' #######################I have defined following things in Global module

Public Declare Function sendMessageByString& Lib "user32" _
Alias "SendMessageA" (ByVal hwnd As Long, _
ByVal wMsg As Long, ByVal wParam As Long, _
ByVal lParam As String) ' pg 239
Public Const LB_SELECTSTRING = &H18C
Public gFindString As String
Public iMsg As Integer