Faild To Enable Constraint?

hey, i have this web form  
http://img175.imageshack.us/img175/6223/12012096.jpg
with drop down menus
everything but the "Hall Number" works (for now )
i used xsd and this is what i wrote to fill the Hall Number
public DataTable GetHallsNumberByCinemaID(int Id) { return hall.GetDataByCinemaID(Id); }
 
this is the xsd query (maybe thats my mistake?)
SELECT        HallNumber
FROM            Hall
WHERE        (CinemaID = @CinemaID)
which works fine, in query builder ofc
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