Operation not supported on read-only collection in Silverlight

Question

Hi All,

I have a Combobox in my Application.The Data is populating into the combo box from database.In the Stored Proc i have given "All" Explicetely.Now i have another combo box in other page in which only data fetching from the database should be populated not "All".So what i did is explecetely removed All by

cmbFeedType.Items.Remove("ALL");

but its throwing an error like "Operation not supported on read-only collection"
can anyone help on this please..

Thanks,
Prasant