Usb port apparently already in use, arduino software

Hello,
My arduino software is giving this error every time I upload something. I have tried different sketches usb cables and usb outputs and none work…

processing.app.SerialException: Serial port '/dev/cu.usbmodem1411' already in use. Try quitting any programs that may be using it.
	at processing.app.Serial.touchPort(Serial.java:119)
	at processing.app.debug.AvrdudeUploader.uploadViaBootloader(AvrdudeUploader.java:203)
	at processing.app.debug.AvrdudeUploader.uploadUsingPreferences(AvrdudeUploader.java:67)
	at processing.app.Sketch.upload(Sketch.java:1671)
	at processing.app.Sketch.exportApplet(Sketch.java:1627)
	at processing.app.Sketch.exportApplet(Sketch.java:1599)
	at processing.app.Editor$DefaultExportHandler.run(Editor.java:2380)
	at java.lang.Thread.run(Thread.java:695)

Any help is appreciated

Michael

THANKS