Install the libgdi+ and I'm still getting this error whenever anyone uses /sil or /silt

Failed to call hook 'SiltCommand' on plugin 'SignArtist v1.2.6' (NullReferenceException: Object reference not set to an instance of an object) at Oxide.Plugins.SignArtist.SiltCommand (Oxide.Core.Libraries.Covalence.IPlayer iplayer, System.String command, System.String[] args) [0x00269] in <e830af4dbdaa4a26805e0f0f5ea22570>:0
at Oxide.Plugins.SignArtist.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x002a3] in <e830af4dbdaa4a26805e0f0f5ea22570>:0
at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <80b90e8213db44b29ec2d4111764172c>:0
at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <ec05e0208c9149bba43236ca58fea105>:0
at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <ec05e0208c9149bba43236ca58fea105>:0