触发器（更新后）导致错误？

我正在使用sql-server 2012，并且编写了这样的触发器：

ALTER TRIGGER [dbo].[ModValue] 
   ON  [dbo].[Table1]
   AFTER UPDATE
AS 
BEGIN
    SET NOCOUNT ON;
    declare @ocid bigint 
    declare @ncid bigint,@pid bigint

    set @ocid=(select CategoryId from deleted)
    select @ncid=CategoryId,@pid=Id from inserted

    if(@ocid<>@ncid)
    begin
    delete from [Table2] where ProductId=@pid
    delete from [Table3] where ProductId=@pid
    delete from [Table4] where ProductId=@pid
    end
END

当我想更新我的表（Table1）时，出现此错误：

消息512，级别16，状态1，过程ModValue，行15
子查询返回的值超过1。当子查询遵循=，！=，<，<=，>，> =或将子查询用作表达式时，不允许这样做。该语句已终止。

更新查询：

update Table1 
set sizing = 0 
where categoryid = 238

该脚本有什么问题？