I had the same problem too with the Demos and I am based in the UK. Unfortunately, I cannot change the regional settings of my machine so other things dont get screwed up.

I am still evaluating for my colleagues and I really like the controls. I didnt want to abandon the controls so I decided to investigate the cause of the error myself. The treeview samples errored because of the american dates in the xml files, so I changed

            this._eventDateTime = x.Attribute("DateTime").Value != null ? DateTime.Parse(x.Attribute("DateTime").Value.Trim()) : DateTime.MaxValue;

to

             this._eventDateTime = x.Attribute("DateTime").Value != null ? DateTime.Parse(x.Attribute("DateTime").Value.Trim(), CultureInfo.InvariantCulture) : DateTime.MaxValue;

in Event.cs and a few other places like FileItem.cs, Email.cs & Task.cs and the treeview samples all worked for me.

Hope this helps.