Serial Port is Busy?

My Arduino Leonardo recently starting sending out this error message every time I try to send anything to the board. I have restarted everything, switched ports, removed anything from the board. I have no idea what I am doing wrong

processing.app.debug.RunnerException
at cc.arduino.packages.uploaders.SerialUploader.uploadUsingPreferences(SerialUploader.java:152)
at cc.arduino.UploaderUtils.upload(UploaderUtils.java:77)
at processing.app.SketchController.upload(SketchController.java:732)
at processing.app.SketchController.exportApplet(SketchController.java:703)
at processing.app.Editor$UploadHandler.run(Editor.java:2042)
at java.lang.Thread.run(Thread.java:748)
Caused by: processing.app.SerialException: Error touching serial port 'COM4'.
at processing.app.Serial.touchForCDCReset(Serial.java:107)
at cc.arduino.packages.uploaders.SerialUploader.uploadUsingPreferences(SerialUploader.java:136)
... 5 more
Caused by: jssc.SerialPortException: Port name - COM4; Method name - openPort(); Exception type - Port busy.
at jssc.SerialPort.openPort(SerialPort.java:164)
at processing.app.Serial.touchForCDCReset(Serial.java:101)
... 6 more