Combobox control problems in a grouped cell
 

I have an Excel sheet.
I have a combobox control in a set of grouped cells. If a click into a
combobox the cursor appears in it. If at this moment I try to collapse
the grouped cells I obtain an Excel error: Integer divided by zero.
In any other cases It works. The problems only appears when we click
into the combobox and the cursor appears in it.
Any idea? Any solution?

Thanks in advanced.

Carles.