ThisWorkbook macros stopped working

I have several Excel 2000 workbooks with vba macros in ThisWorkbook controlling what happens when a workbook is opened, activated or closed. These workbooks are in use by several users on different PCs and all macros were working fine with no problems whatsoever.

Suddenly, they no longer work on any PC for any user. For now I have had to use the old method of Sub Auto_open() and Sub Auto_close() in the main module.

So I have two questions:

1. Does anyone know of a security patch or similar that could stop macros in ThisWorkbook from running?
2. Does anyone know of an alternative to ThisWorkbook "Sub Workbook_Activate()" macro that I could use in the main module?

Thanks