На таком валидном regexe Решарпер 9.1 даёт ошибку Unexpected token.

private static Regex _whereItemRegex = new Regex(@"
        (?<exproperator>AND|OR)?                                                                            # expression operator
        (?:\s*\(*)\s*                                                                                       # whitespaces
            (?<fieldName>\w+)                                                                               # fieldname
            \s*(?<operator>=|<>)\s*                                                                            # operator
            (?<quotedvalue>                                                                                    # quoted value
                                '(?<value>[^']*)'                                                           # string value
                                |   (?<value>[+-]?(?:[0-9]*\.?[0-9]+|[0-9]+\.?[0-9]*)(?:[eE][+-]?[0-9]+)?)    # number
                                |   \#(?<value>[^#]+)\#                                                     # datetime value
            )(?:\s*\)*\s*)                                                                                    # whitespaces
            ", RegexOptions.Compiled | RegexOptions.Multiline | RegexOptions.IgnorePatternWhitespace);