Can not upload to MKR FOX 1200 - COm port busy

Dear All,

I have uploaded a sketch to the MKR FOX 1200 and it works well, but I have made some changes to the code and now each time to try I get the following error:

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:2047)
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

I have rebotted the PC several times, restarted Arduino app and reset the board. I have dsicnnected all the pins from the device but nothing makes any difference.

Having read the guides on here, I have also disabled the bluetotth adaptor I have and and vitrual com ports.

Any help will be appreciated as I am stuck at the moment.

Andrew