Arduino UNO suddenly not uploading any more

I get the following error

processing.app.debug.RunnerException
at cc.arduino.packages.uploaders.SerialUploader.uploadUsingPreferences(SerialUploader.java:160)
at cc.arduino.UploaderUtils.upload(UploaderUtils.java:78)
at processing.app.SketchController.upload(SketchController.java:713)
at processing.app.SketchController.exportApplet(SketchController.java:686)
at processing.app.Editor$DefaultExportHandler.run(Editor.java:2168)
at java.lang.Thread.run(Thread.java:748)
Caused by: processing.app.SerialException: Error touching serial port 'COM5'.
at processing.app.Serial.touchForCDCReset(Serial.java:107)
at cc.arduino.packages.uploaders.SerialUploader.uploadUsingPreferences(SerialUploader.java:144)
... 5 more
Caused by: jssc.SerialPortException: Port name - COM5; Method name - openPort(); Exception type - Port busy.
at jssc.SerialPort.openPort(SerialPort.java:164)
at processing.app.Serial.touchForCDCReset(Serial.java:101)
... 6 more
Problem uploading to board. See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.
Exception in thread "Thread-63" java.util.ConcurrentModificationException
at java.util.LinkedList$LLSpliterator.forEachRemaining(LinkedList.java:1239)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151)
at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:418)
at cc.arduino.contributions.libraries.LibrariesIndexer.rescanLibraries(LibrariesIndexer.java:127)
at cc.arduino.contributions.libraries.LibrariesIndexer.setLibrariesFolders(LibrariesIndexer.java:106)
at processing.app.BaseNoGui.onBoardOrPortChange(BaseNoGui.java:682)
at processing.app.Base.onBoardOrPortChange(Base.java:1313)
at processing.app.Editor$DefaultExportHandler.run(Editor.java:2198)
at java.lang.Thread.run(Thread.java:748)

Any help or directions greatly appreciated!

Exception Type: Port Busy.

That means another program is using the serial port. Close the other program. If you can't identify this program, reboot the system.

Are you using the web editor? I'm just wondering about the processing word in your error message.

I've installed the Desktop App for Windows