DropDownList Validation not working inside Gridview

I have a dropdownlist inside a gridview,the drop list should populate from database and default value should be SELECT.

when i Click Save button it should check all the dropdownlist values. If any one is still SELECT it should prompt error select any values.

When i normaly check without inside gridview it works fine and not inside gridview.

I have attached my codings below.

Help in this regard.

Thanks