Try this code:
public static Regex regex = new Regex(
"\\<returns\\>([^\\<]*)\\</returns\\>",
RegexOptions.IgnoreCase
| RegexOptions.Singleline
| RegexOptions.CultureInvariant
| RegexOptions.IgnorePatternWhitespace
| RegexOptions.Compiled
);
Get a copy of Expresso - it is free and really helps!