My Big Problem....

[opus]

I Have no idea why the testoutfile.txt should be empty.
There is a mistake in the code, it uses all lines with "solution" imnstead of those without.

I changed it:

Dim DatNr1 As Integer
    Dim DatNr2 As Integer
    Dim strTextLine As String
    Dim ret As Integer
    DatNr1 = FreeFile
    Open "outfile.txt" For Input As DatNr1
    DatNr2 = FreeFile
    Open "testoutfile.txt" For Output As DatNr2
    Do While Not EOF(DatNr1)
       Input #DatNr1, strTextLine
 
       ret = InStr(1, LCase(strTextLine), "solution")
       If ret = 0 Then
          Write #DatNr2, strTextLine
       Else
          Write #DatNr2,
       End If
    Loop
    Close #DatNr1
    Close #DatNr2

the resulting file I get when using your "outfile.txt" is attached!