Serial port '/dev/tty.usbmodem411' already in use

I tried the following steps but Im still stucked.

That's the second time this happens. I bought this one because of the same issue. I thaught it was a bad supplier or something.

Is this hardware issue?

Thanks for any help.

Arduino UNO R3. Mac OS X, 10.7.5

/var/folders/yj/nj8vb1k17glbzjcnhcsd9nmr0000gn/T/build4861594367447780835.tmp/sketch_aug20a.cpp.elf /var/folders/yj/nj8vb1k17glbzjcnhcsd9nmr0000gn/T/build4861594367447780835.tmp/sketch_aug20a.cpp.hex
Binary sketch size: 1,744 bytes (of a 32,256 byte maximum)
processing.app.SerialException: Serial port '/dev/tty.usbmodem411' already in use. Try quiting any programs that may be using it.
at processing.app.Serial.(Serial.java:171)
at processing.app.Serial.(Serial.java:77)
at processing.app.debug.Uploader.flushSerialBuffer(Uploader.java:77)
at processing.app.debug.AvrdudeUploader.uploadViaBootloader(AvrdudeUploader.java:175)
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$DefaultExportHandler.run(Editor.java:2380)
at java.lang.Thread.run(Thread.java:695)
processing.app.debug.RunnerException: Serial port '/dev/tty.usbmodem411' already in use. Try quiting any programs that may be using it.
at processing.app.debug.Uploader.flushSerialBuffer(Uploader.java:101)
at processing.app.debug.AvrdudeUploader.uploadViaBootloader(AvrdudeUploader.java:175)
at processing.app.debug.AvrdudeUploader.uploadUsingPreferences(AvrdudeUploader.java:67)
at processing.app.Sketch.upload(Sketch.java:1671)
at processing.app.Sketch.exportApplet(Sketch.java:1627)
at processing.app.Sketch.exportApplet(Sketch.java:1599)
at processing.app.Editor$DefaultExportHandler.run(Editor.java:2380)
at java.lang.Thread.run(Thread.java:695)
processing.app.SerialException: Serial port '/dev/tty.usbmodem411' already in use. Try quiting any programs that may be using it.
at processing.app.Serial.(Serial.java:171)
at processing.app.Serial.(Serial.java:92)
at processing.app.SerialMonitor.openSerialPort(SerialMonitor.java:207)
at processing.app.Editor.handleSerial(Editor.java:2481)
at processing.app.Editor$17.actionPerformed(Editor.java:665)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2028)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2351)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.AbstractButton.doClick(AbstractButton.java:389)
at com.apple.laf.ScreenMenuItem.actionPerformed(ScreenMenuItem.java:95)
at java.awt.MenuItem.processActionEvent(MenuItem.java:650)
at java.awt.MenuItem.processEvent(MenuItem.java:609)
at java.awt.MenuComponent.dispatchEventImpl(MenuComponent.java:343)
at java.awt.MenuComponent.dispatchEvent(MenuComponent.java:331)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:720)
at java.awt.EventQueue.access$400(EventQueue.java:82)
at java.awt.EventQueue$2.run(EventQueue.java:676)
at java.awt.EventQueue$2.run(EventQueue.java:674)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:86)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:690)
at java.awt.EventQueue$3.run(EventQueue.java:688)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:86)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:687)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)