Board Thread:Help!/@comment-26358592-20200222211156

Whenever I try to open my game, it brings up this:

System.IndexOutOfRangeException: Imdex was outside the bounds of the array. at Terraria.Procs.NpcMask.get_Item(Int32 index) at Terraria.Event.b_12 at Terraria.Event.UpdateEvents at Terraria.Procs.UpdateBegin at Terraria.Main.Update(GameTime gameTime) at Microsoft.Xna.Framework.Game.RunGame(BooleanuseBlockingRun) at Terraria.Program.InitializeGame(Int32 Choices) at Terraria.LaunchGame(String[] args)

Before this, the game worked just fine. Any help? 