Because the problem is not caused by a missing COM error but by an AutoIt bug. In the first post the problem is caused when accessing a property of an object that doesn't exist. Add the following function to your script and replace _Excel_BookOpen with _Excel_BookOpenEX. Func _Excel_BookOpenEX($oExcel, $sFilePath, $bReadOnly = Default, $bVisible = Default, $sPassword = Default, $sWritePassword = Default, $bUpdateLinks = Default)     ; Error handler, automatic cleanup at end of