Megas stopped uploading

Development Tools IDE 1.x
1

I have 2 Megas, an Uno, and 2 PCs. Until yesterday all Arduinos worked with both PCs. Now I can still use the Uno with either PC but both Megas won't upload. After several minutes I get the error messages:

avrdude: stk500v2_ReceiveMessage(): timeout
avrdude: stk500v2_getsync(): timeout communicating with programmer
over and over.

However I can load simple programs into the Megas using Codebender instead of the Arduino IDE, so the hardware must be OK. But Codebender doesn't have the latest Adafruit libraries.

I have been using Arduino 1.6.4 for a long time. I don't know why it suddenly broke on two separate PCs.

2

You didn't by any chance put a string containing three exclaimation points into your sketch did you? Some Megas have a bootloader with a bug that causes it to hang when it sees "!!!" in uploaded code.

3

(deleted)

4

Three exclamation points was the culprit!!! I would never have suspected that on my own. What a bizarre bug! Also once a download fails it seems the PC com port is broken until the PC reboots, so simply editing the code and retrying didn't work.

Thank you very much DrAzzy and the Forum in general!