Dropdown List problem

Hi i'm a newbie

I have a large (>10mb) spreasheet with 20+ tabs. Every tab has a number of formulas linked to other tabs.

On one of the tabs i have a list of countries (A2:A32)

On another tab i have a dropdown box which list the counties defined in A2:A32. Fo good measure I defined A2:A32 as a named range 'countries'

That dropdown is in A27. A27 is embedded in DOZENS of formulas so data changes dependant on the selected country in A27.

My problem is that the dropdown keeps losing its listdata randomly.

I have got round the problem by using a formcontrol combobox from the 'Developer > Insert Controls' menu. BUT that dropdown floats and isnt tied to A27 some my other formulas dont work.

I'm using EXCEL 2010, My users will use 2003-2010.

Can anyone help please

Thanks but i've solved it using http://support.microsoft.com/kb/291073

Thnx anyway