Help PLEASE!!!

[joi2]

I am having problems with this code every time I run the code I get an error when this loop runs. what I am trying to do is pick up anything that appears between the words application and platform for example (platform blah, blah, blah, application)and when i run the loop after it finds the first case it gives me an error saying "Ivalid procedure call or argument". heres a copy of the code an i=2105 and j=553

Sub test1()
    Dim r As Range
    Dim rword As Range
    Dim h As Long, l As Long
    Dim xlApp As Excel.Application
    Dim xlWB As Excel.Workbook
    
'With ActiveDocument
    Dim seastring1 As String
    Let seastring1 = ThisDocument.Content
    
    Const seastring2 As String = "Application:"
    Const pook As String = "Platform:"
    
    


 
Dim j As Long
Dim i As Long

j = InStr(seastring1, seastring2)
i = InStr(1, seastring1, pook)
Do While i <> 0





MsgBox Mid$(seastring1, i, j - i), Len(Mid$(seastring1, i, j - i))
'MsgBox pook & i
'MsgBox Mid$(seastring1, i, InStr(seastring1, seastring2) - i) ', Len(Mid$(seastring1, i, InStr(seastring1, seastring2) - i ))
i = InStr(i + 1, seastring1, pook)

Loop
'End With
End Sub