cannot upload a sketch to Arduino YUN [SOLVED]

Hello,

I bought my Arduino YUN today and some basic sketches worked perfectly.

Unfortunately I cannot upload sketches anymore.

I got this error:
Sketch uses 4.744 bytes (16%) of program storage space. Maximum is 28.672 bytes.
Global variables use 151 bytes (5%) of dynamic memory, leaving 2.409 bytes for local variables. Maximum is 2.560 bytes.
avrdude: AVR device not responding
avrdude: initialization failed, rc=-1
** Double check connections and try again, or use -F to override**
** this check.**

When my YUN is started, these LEDs are on:
yellow RX
red L13
green ON
white USB

I upload my sketches over WIFI

WIFI and linux-chip do work, i can connect to the website, and can connect to the LINUX-chip with SSH - putty

I've tried to reset WIFI, 'YUN RST' and the 32u4, but that didn't solve the problem

Can somebody help me ? many thanks !

Solved: went back to the shop, 32u4 was broken, got a new one.