Failed to run command '/bgrade' on plugin 'BGrade'. (FormatException: Index (zero based) must be greater than or equal to zero and less than the size of the argument list.)
at System.Text.StringBuilder.AppendFormatHelper (System.IFormatProvider provider, System.String format, System.ParamsArray args) [0x000f9] in <47fc8c70fa834cbf8141d7c1a7589125>:0
at System.String.FormatHelper (System.IFormatProvider provider, System.String format, System.ParamsArray args) [0x00023] in <47fc8c70fa834cbf8141d7c1a7589125>:0
at System.String.Format (System.String format, System.Object[] args) [0x00020] in <47fc8c70fa834cbf8141d7c1a7589125>:0
at Oxide.Plugins.BGradeExt.BGradeExtensions.Lang (System.String key, System.String id, System.Object[] args) [0x00011] in <f3ab56cc010b4a1f9ffc3fe24fc2be0a>:0
at Oxide.Plugins.BGrade.BGradeCommand (BasePlayer player, System.String command, System.String[] args) [0x001f1] in <f3ab56cc010b4a1f9ffc3fe24fc2be0a>:0
at Oxide.Game.Rust.Libraries.Command+ChatCommand.HandleCommand (BasePlayer sender, System.String name, System.String[] args) [0x0001b] in <5649bb583fc240c485ad6ee701cbac60>:0
at Oxide.Game.Rust.Libraries.Command.HandleChatCommand (BasePlayer sender, System.String name, System.String[] args) [0x00015] in <5649bb583fc240c485ad6ee701cbac60>:0
at Oxide.Game.Rust.RustCore.TryRunPlayerCommand (BasePlayer basePlayer, System.String message, System.String commandPrefix) [0x000c2] in <5649bb583fc240c485ad6ee701cbac60>:0

The error you're getting is from the BGrade plugin. This's BuildingGrades