Assign Macro to Button

I am using Excel 2003 on Vista. I have a custom button on a tool bar. I have assigned a macro to it that is in the Personal.xls workbook. It was working fine. From another workbook with the tool bar visible, I clicked the button and the macro executed. All was fine. At one point for some unknown reason, the button no longer activates the macro. When I try to redo the assign macro to the button, the macro is listed in the list (as being in the Personal.xls workbook). I click to select it. The macro name is then listed at the top of the Assign Macro dialog box (as normal) . I click ok to exit. However, when I subsequently click the button with the newly (re)assigned macro, the macro does not run and the assign macro dialog box displays presumable asking me to assign a macro to the button. The assignment that I did apparently didn't take. Why? If I do the (re)assignment and then just go back to the assign macro dialog, it's not there either. Other facts: While I do the assign the Personal.xls workbook is open and unhidden. The assign was working at one point and suddenly is not. The module that the macro is in contains multiple subs and functions. I have checked that they all have matching end statements. The module is in development/debug so it is reasonable to believe I have something in the macro/module that is a cause. Although, the macro is successfully listed in the list of macro's to choose from in the assign macro dialog. I have also tried deleting the button from the tool bar and recreating it. That didn't help. The macro runs successfully in debug mode where I click F5 in the VBA editor.

Help please!