Downloading a replay from my track or anyone else's track gives me this error. Right after I get the dialog "Mania Code Complete" I get another dialog saying " Could Not Determine Title To Use" What's up with that? If this has been discussed already, I was unable to find the tread.

Think it is a bug not yet fixed from Nadeo. Before, we could just download a replay and set the browser to automatically open when finish. And click any replays to view or race against. But that do not work anymore. So the way u have to do it is to download it, then start MP, and from the right title, go to "local play", then "versus replay", then go in the right folder and click the replay and "launch".....

Hope this helps....

Yes, Nesrally is correct. This is an error from Nadeos side.
You will get the same error if you double-click a Replay.Gbx file from your windows explorer.