Enabling formulas in a semi-protected sheet
 

Hi

I have coded some interaction with Excel 2003 from a C#-application.
I have protected an area of a sheets and another area is unprotected in the same sheet.
When I open the semi-protected sheet, it is not possible to use formulas in the unprotected area - ie. the Autosum-button is disabled and so are other buttons in the toolbar.
How can I enable formulas in my C#-code?