drop down list selected value error

Hi all,

I've got a drop down list which gets populated bu a PopulateDropDown() in a UIHelper.cs.

The ddl has been inserted with a -select category- list item with value of "-1". When i want to select this item i get this error

"'ddlKeyIndustry' has a SelectedValue which is invalid because it does not exist in the list of items. Parameter name: value"

Any ideas?
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