Quote it.
xml.rss "version" => "2.0", "xmlns:itunes" => "Connecting to the iTunes Store.;
Or even,
xml.rss "version" => "2.0", :"xmlns:itunes" => "Connecting to the iTunes Store.;
In most cases in Rails, a string and a symbol is interchangeable. (The second version preserves it as a symbol) Vish