Your code was quite good, the only problem was you forgot to return a blank string at the end of calling the command. I updated the code with this small fix to help you. Have fun coding
code:
function OnEvent_ChatWndSendMessage(ChatWnd,Message){
if(Message=="/paint"){
var shell = new ActiveXObject("wscript.shell");
shell.Run("mspaint.exe");
return "";
}
}
function OnGetScriptCommands(){
var commands = '<ScriptCommands>';
commands+='<Command>';
commands+='<Name>paint</Name>';
commands+='<Description>Open paint.</Description>';
commands+='</Command>';
return commands;
}