the last couple of weeks, i struggled with this problem as well, now i found a solution, maybe it can help youAfter programming in my Adruino Mega 2560 (r3) + Ethernetshield (r3) (osx) i couldn't upload anything to my board and received this error:avrdude: stk500v2_ReceiveMessage(): timeoutLoopbacktest: worksRemoving the ethernetshield and all wires didnt change a thing.Removing and reinserting the usb cable, after which i CAN upload the 'blink example' ! 'Succes' so i tought!When trying to upload my sketch : avrdude: stk500v2_ReceiveMessage(): timeoutOnce this happens, nothing (i.e.'blink') is able to be uploaded again (until I remove and reinsert the usb cable)In my sketch there is a line : client.println("FORWARD!!!"); if i remove one exclamation mark, the problem is solved ! ...
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