System.ArgumentException: An item with the same key has already been added解决思路

System.ArgumentException: An item with the same key has already been added
碰到exception:   System.ArgumentException:   An   item   with   the   same   key   has   already   been   added,   哪位知道这是哪里出了问题吗？

[解决办法]
翻译过来就明白了。
key已经存在