Excel 2003 Exits when you try closing a workbook

We have a couple of users (Hp laptops, XP, Office 2003)who, when working in Excel 2003, and select file>close (or the x) it is exiting all of Excel, instead of just closing that workbook. There are no error messages, Excel is jut exiting. These users do have Adobe Acrobat 7 in common, and Adobe is patched to the latest version.