c# - Unity3d Google Play Games InvalidCastException: Cannot cast from source type to destination type -

i'm taking error in unity3d editor:

invalidcastexception: cannot cast source type destination type. leaderboardfunctions.show_coins_leaderboard () (at assets/leaderboardfunctions.cs:53) 

but strange because used same code other project project coming that.

((playgamesplatform)social.active).showleaderboardui(leaderboard.leaderboard_highscores); playgamesplatform giving error.