Ok... are there numbers in rows 103, 104, etc? because your code is correct. However, a much simpler version:

Sub clear()

Dim i as Long

For i = 102 to 114
    If Application.WorksheetFunction.Sum(Sheets("Invulblad").Range(Sheets("Invulblad").Range("L" & i), Sheets("Invulblad").Range("S" & i))) > 0 Then Sheets("Chemicalien").Range("O" & i - 99).Value = ""
Next i

End Sub
Please provide a workbook if you still have problems. Include the 2 sheets, and the data that is in there when it is not working.

To Attach a sample workbook (not a picture or pasted copy). Make sure there is just enough data to demonstrate your need.

Remember to desensitize the data.

Click on GO ADVANCED and then scroll down to Manage Attachments to open the upload window.