Arduino Due Port Not Found

I've got an arduino due and I'm having great difficulty connecting to it. The problem seems to come and go, I was using it just fine only 3 or 4 hours ago but now it just won't connect. I've got the board set to the Arduino Due Native Port and the port set to the /dev/cu.usbmodem1421 (Arduino Due Native Port). Every time I try and upload the sketch however, it gives me this error:

    Arduino: 1.6.6 (Mac OS X), Board: "Arduino Due (Native USB Port)"

Sketch uses 10,316 bytes (1%) of program storage space. Maximum is 524,288 bytes.
processing.app.debug.RunnerException
    at cc.arduino.packages.uploaders.SerialUploader.uploadUsingPreferences(SerialUploader.java:130)
    at cc.arduino.UploaderUtils.upload(UploaderUtils.java:78)
    at processing.app.Sketch.upload(Sketch.java:1178)
    at processing.app.Sketch.exportApplet(Sketch.java:1152)
    at processing.app.Sketch.exportApplet(Sketch.java:1124)
    at processing.app.Editor$DefaultExportHandler.run(Editor.java:2452)
    at java.lang.Thread.run(Thread.java:745)
Caused by: processing.app.SerialException: Error touching serial port '/dev/cu.usbmodem1421'.
    at processing.app.Serial.touchForCDCReset(Serial.java:87)
    at cc.arduino.packages.uploaders.SerialUploader.uploadUsingPreferences(SerialUploader.java:119)
    ... 6 more
Caused by: jssc.SerialPortException: Port name - /dev/cu.usbmodem1421; Method name - openPort(); Exception type - Port not found.
    at jssc.SerialPort.openPort(SerialPort.java:167)
    at processing.app.Serial.touchForCDCReset(Serial.java:81)
    ... 7 more
Error opening serial port '/dev/cu.usbmodem1421'. (Port not found)

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