Henry Cabot Lodge's Objections to Article 10 of the Treaty of Versailles (1919)Why do you think the Senate was more receptive to these arguments in...

To me, the major difference here is that, in 1945, the US was essentially in control of the making of the United Nations and could set it up as they wanted. In addition, I think that they used this power to set the UN up in a way that would not have the same "problems" that the League of Nations had.

Specifically, the UN was set up so that the five permanent members of the Security Council each had a veto on any action taken by that Council.  This meant that any of the five countries (including the US) could veto a military action by the Security Council.  That way, the US could not be dragged into a war against its will in the way that it might have been under the League of Nations.