"'MIDI' was not declared in this scope" - Please help.

I´m trying to get an already existing code to work with my Arduino Uno (I´m a newbie).
I have installed the latest version of the midi-library. But something is wrong. Anyone know what to do?

This is the error message I get:

sketch_feb20h.ino: In function 'void loop()':
sketch_feb20h.ino:77:2: error: 'MIDI' was not declared in this scope

And this is the code I'm using:

// MIDI THEREMIN
// Moritz Simon Geist
// www.sonicrobots.com
// v.1.0 14 March 2014
////////////////////////////////
// This sketch uses an HC-SR04 Ultrasonic Sensor and produces an MIDI out signal, according to the measured distance form a object
// Be sure to include the latest MIDI Library (here 4.0)
// Arduino Playground - MIDILibrary
//
// Wiring: Ping pin from the HC-SR04 Ultrasonic Sensor --> arduino Pin 13,
// Echo pin from HC-SR04 Ultrasonic Sensor --> Arduino PIN 12
// MIDI-Out --> TX according to this sketch http://arduino.cc/en/uploads/Tutorial/MIDI_schem.png

#include <MIDI.h>
int pingPin = 13;
int inPin = 12;
long duration;
int cm_new = 20;
int cm_old = 20;
int sens = 5; // sensivity range when to launch a new note

void setup() {

Serial.begin(31250); // MIDI Begin
pinMode(pingPin, OUTPUT); // setup the Pins
pinMode(inPin, INPUT); // setup the Pins

}

void loop()
{

// The PING is triggered by a HIGH pulse of 2 or more microseconds.
// Give a short LOW pulse beforehand to ensure a clean HIGH pulse:

digitalWrite(pingPin, LOW);
delayMicroseconds(2);
digitalWrite(pingPin, HIGH);
delayMicroseconds(10);
digitalWrite(pingPin, LOW);
duration = pulseIn(inPin, HIGH); // the singal from the Sensor is measured. The length of the pulse describes the distance form an object to the sensor.

cm_new = map(constrain(duration, 20, 3000), 50, 2000, 96, 48); // contrain --> set a threshold to cut values of the sensor that are to far away of to short (20 .. 3000) MAP --> Map the sensor range to a note values vom 96 (A high C) to 48 (a low C)

if (cm_new != cm_old) // only if a new sensor value is detected, a new nite will be send. IF the object stays stable infront of the sensor, no note will be send.
{
MIDI.sendNoteOff(cm_old,0,1); // Stop the old note
MIDI.sendNoteOn(cm_new,127,1); // Send a new Note (pitch , velocity 127, on channel 1)
cm_old = cm_new;
}
delay(30); // for staiblity
}

I have installed the latest version of the midi-library. But

I'm not going to tell you where...

PaulS:
I'm not going to tell you where...

I downloaded the .zip-file and added that file via the "add library" in the IDE

Well, OK. Then it should have worked.

Since it didn't, you obviously did something wrong (or the library packagers did). But, since you didn't tell us where you got the library from, or exactly what you did, we can't help.

I got the library from here:

Maybe you know another one?
The library has been added and is visible in the library-list. But yet it doesnt work. Maybe it's damaged or wrong in some way...

I got the library from here:

If came with examples that show that you missed a key function call.

PaulS:
If came with examples that show that you missed a key function call.

Oh. Allright. I´ll look it up. Missed it. Everything is very new in this arduino-world to me...