Arduino YÚN - unable to upload anymore

Hi,

I got my YÚN board in mid september and did a lot of work with it but yesterday it stopped working properly. Here are the facts of the status quo:

  • Working with Arduino IDE 1.5.4 and had no problem all the time (about 3 months)
  • Tried the IDE 1.5.5 but same problem
  • The board still powers on and runs the last uploaded code
  • The TX LED is all the way on and fades up and down fast and unfrequently (not blinking)
  • The computer recognises the board when I plug it into the USB port
  • The Arduino IDE shows the correct board on the COM port
  • After pressing "upload" in the Arduino IDE the sketch compiles and the RX LED is blinking a few times and about 1 minute later the IDE shows up this error:
Found programmer: Id = "Bz3"; type = 
Software Version = . ; Hardware Version = .
avrdude: error: buffered memory access not supported. Maybe it isn't
a butterfly/AVR109 but a AVR910 device?
processing.app.debug.RunnerException
    at cc.arduino.packages.uploaders.SerialUploader.uploadUsingPreferences(SerialUploader.java:129)
    at processing.app.Sketch.upload(Sketch.java:1672)
    at processing.app.Sketch.exportApplet(Sketch.java:1578)
    at processing.app.Sketch.exportApplet(Sketch.java:1550)
    at processing.app.Editor$DefaultExportHandler.run(Editor.java:2399)
    at java.lang.Thread.run(Unknown Source)
Caused by: processing.app.debug.RunnerException: Probleme beim Hochladen auf das Board. Hilfestellung dazu unter http://www.arduino.cc/en/Guide/Troubleshooting#upload .
    at cc.arduino.packages.Uploader.executeUploadCommand(Uploader.java:113)
    at cc.arduino.packages.uploaders.SerialUploader.uploadUsingPreferences(SerialUploader.java:127)
    ... 5 more

I never had this kind of problem with an Arduino board so I'm really afraid of a defect on my very young YÚN. I never "burned a bootloader" or reprogrammed a board so would this http://arduino.cc/en/Tutorial/ArduinoISP probably solve my issue?

Any help is much appreciated, thanks!