Changing the firmware for dual extrusion: serial port error

Hello,

I recently bought a second printhead. Everything went smooth till I needed to upload my firmware. I used Arduino version 1.0.6 like you guys recommend but still received the problem that my serial port where my printer was connected to was occupied. I checked if that was true and it was but it was connected to the arduino itself, so I tried to restart the whole process. But still no progress. I still get this message:

This report would have more information with
“Show verbose output during compilation”
enabled in File > Preferences.
Arduino: 1.0.6 (Windows NT (unknown)), Board: “Arduino Mega 2560 or Mega ADK”
Binaire sketch-grootte: 128.606 bytes (van een 258.048-byte maximum)

processing.app.SerialException: Seriële poort ‘COM3’ is reeds in gebruik. Sluit de programmas die de poort gebruiken af.

at processing.app.Serial.<init>(Serial.java:171)

at processing.app.Serial.<init>(Serial.java:77)

at processing.app.debug.Uploader.flushSerialBuffer(Uploader.java:77)

at processing.app.debug.AvrdudeUploader.uploadViaBootloader(AvrdudeUploader.java:175)

at processing.app.debug.AvrdudeUploader.uploadUsingPreferences(AvrdudeUploader.java:67)

at processing.app.Sketch.upload(Sketch.java:1666)

at processing.app.Sketch.exportApplet(Sketch.java:1622)

at processing.app.Sketch.exportApplet(Sketch.java:1594)

at processing.app.Editor$DefaultExportHandler.run(Editor.java:2382)

at java.lang.Thread.run(Thread.java:619)

processing.app.debug.RunnerException: Seriële poort ‘COM3’ is reeds in gebruik. Sluit de programmas die de poort gebruiken af.

at processing.app.debug.Uploader.flushSerialBuffer(Uploader.java:101)

at processing.app.debug.AvrdudeUploader.uploadViaBootloader(AvrdudeUploader.java:175)

at processing.app.debug.AvrdudeUploader.uploadUsingPreferences(AvrdudeUploader.java:67)

at processing.app.Sketch.upload(Sketch.java:1666)

at processing.app.Sketch.exportApplet(Sketch.java:1622)

at processing.app.Sketch.exportApplet(Sketch.java:1594)

at processing.app.Editor$DefaultExportHandler.run(Editor.java:2382)

at java.lang.Thread.run(Thread.java:619)

Can you help me with this?

thanks alot!