After you install Microsoft Office 2003 Service Pack 3 (SP3), you cannot open Microsoft Excel 5.0/95 Workbook files that contain Microsoft Visual Basic for Applications (VBA) macros in Microsoft Office Excel 2003
If the macro security level is set to High or to Very High, you may receive the following error message:
This workbook cannot be opened under High Security Level because it contains a type of macro (Microsoft Excel 4.0 macro) that cannot be disabled or signed.
If the macro security level is set to Medium, you may unexpectedly be prompted to enable the macros or to disable the macros.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Microsoft has increased the level of security for VBA macros in Microsoft Excel 5.0/95 Workbook files in Office 2003 SP3. This change provides more control for you to determine which macros will run. Additionally, this change helps prevent security attacks on earlier file formats.