Using XMLRPC from Delphi

Hi! I want to create my own XMLRPC client. But I have a some trouble…
I test my client with method “wp.newCategory” and my parameters are blog_id, user name, user pass, and then must bea array with name, description, slug and parent_id.
The problem in Array. How I to have to use this paremeter?

I use DXmlRpc paccague for delphi.
See some of my code:

RpcFunction := TRpcFunction.Create;
    RpcFunction.ObjectMethod := 'wp.newCategory';
    RpcFunction.AddItem(1);
    RpcFunction.AddItem('admin');
    RpcFunction.AddItem('pass');

arr := TRPCArray.Create;
arr.AddItem('name:dd');
RpcFunction.AddItem(arr);

RpcResult := RpcCaller.Execute(RpcFunction);

When I use this code, I recive error that a last paremeter(array) is not string.